Montigny Mission

In October 1855,^[1] Emperor Napoleon III of the Second French Empire appointed Charles de Montigny as the French imperial plenipotentiary to negotiate for a new commercial treaty with the Kingdom of Siam, to remonstrate the issue of Vietnamese persecution of Catholics and to conclude a new treaty with Nguyen-dynasty Vietnam.^[2]: 404 Montigny arrived in Siam, in Bangkok, in July 1856^[1] during the reign of King Mongkut of Siam, where he successfully concluded the Franco-Siamese Treaty of August 1856.^{[3] : 87}After staying in Siam for two months, Montigny left for Cambodia in September 1856^[4]: 183 where, due to many obstacles and the Siamese intervention,^[5] Montigny was unable to meet King Ang Duong of Cambodia at Oudong. During his stay in Kampot, Montigny preliminarily sent two French corvettes to Vietnam, during the reign of Emperor Tự Đức. Vietnam's stern refusal to receive the French diplomatic letter resulted in the French bombardment of Danang in September 1856.^[4]: 188 After many unsettling issues, Montigny did not manage to conclude a treaty with Cambodia and was obliged to left for Vietnam, where Montigny arrived at Danang (also called Tourane) in January 1857.^[4]: 188 Montigny's negotiation with the Vietnamese imperial court also resulted in failure.^[4]: 197 Montigny left Vietnam with contempt, threatening Vietnam with military intervention. Montigny's diplomatic mission to three Southeast Asian polities, namely Siam, Cambodia and Vietnam, from mid-1856 to early 1857, marked the advent of impactful French presence in the region, leading to the French conquest of Cochinchina and Franco–Siamese dispute over Cambodia in the 1860s.

At the conclusion of the Siamese–Vietnamese War in 1847, King Harireak Reamea Ang Duong was enthroned with both Siamese and Vietnamese endorsements as Ang Duong was obliged to pay tributes to both Siam and Vietnam.^[5] The Cambodian king Ang Duong then sought for an external Western power to protect Cambodia from both Siam and Vietnam.^[5] Bishop Jean-Claude Miche the Apostolic Vicar of Cambodia, on behalf of Ang Duong, wrote a letter to Gauthier the French Consul at Singapore, proposing to establish the Franco–Cambodian relation.^[6] The letter reached Singapore in December 1852.^[6] Gauthier the French Consul, however, was not committed to the cause. Sir John Bowring the British plenipotentiary concluded the Bowring Treaty with Siam in April 1855.^[3]: 73 In October 1855, Charles de Montigny was appointed as the French plenipotentiary to conclude a treaty with Siam in similar manner with the British.^[1] Montigny reached Singapore in May 1856,^[1] where he was assigned additional missions to deal with the Vietnamese persecution of Catholics, to conclude a similar commercial treaty with Vietnam^[1] and also to inform King Ang Duong of Cambodia that his gifts had not yet reached France.^[6] Siamese government, who regarded Cambodia as its vassal, was largely unaware of this discreet Cambodian contact with France.^[5]

Montigny arrived in Bangkok in July 1856 with French corvettes Marceau, Catinat and Capricieuse.^[4]: 188 Montigny was received by the Siamese royal court in grand ceremonies at the Siamese royal palace. During Montigny's negotiations in Siam, Montigny asked the Siamese king Mongkut about Cambodia and asked for Khmer translators. The Siamese then realized that Cambodia had been in confidential contact with France and sought to prevent Cambodia from establishing relations with France.^[5] Montigny also sent corvette Catinat under the command of Le Lieur to Vietnam for survey. The Franco–Siamese "Montigny Treaty" was successfully concluded at Bangkok on 15 August 1856.^{[1][2]: 378 [3]: 87}

French corvette Catinat under Le Lieur reached Danang in September 1856.^[4]: 188 Le Lieur sent a French priest Charles Fontaine^[4] to present a French diplomatic letter to the Vietnamese authorities at Danang, who refused to receive the letter. Le Lieur then propelled Catinat into the Perfume River to present the letter to the Vietnamese at Huế, where the Vietnamese Emperor resided. The Vietnamese again refused to take the letter, leaving the letter on the beach.^[4]: 188 Enraged, Le Lieur delivered an ultimatum. As Vietnam remained unresponsive, Le Lieur bombarded Danang with cannons from Catinat.^[4]: 188 On 26 September 1856, Le Lieur led French marines in an amphibious assault on Danang. The Vietnamese in Danang suffered damages and casualties in this French attack. Emperor Tự Đức responded by organizing defenses under the Vietnamese commander Đào Trí.^[7]

After the conclusion of the treaty with Siam, Montigny left Siam for Cambodia in September 1856,^[4]: 183 taking some Khmer men and the translators with him on Capricieuse to Cambodia. At his own initiative, Montigny intended to make a treaty with Cambodia. However, among the passengers were three Siamese spies.^[5] Upon Montigny disembarkation at Kampot in October, the Siamese agents coerced the Cambodian officials in Kampot not to agree to any French proposals.^[5] Bishop Jean-Claude Miche helped Montigny uncovered these Siamese agents, who were chased away by Montigny. Montigny also sent corvette Capricieuse under Collier to join with Le Lieur in Vietnam.^[4] Montigny demanded that the Cambodian king Ang Duong come to meet him at Kampot to conclude a treaty. Ang Duong, in turn, invited Montigny to take the road from Kampot to Oudong to meet him. However, Montigny was unwilling to go to Oudong as he was late in his due arrival in Vietnam, where his main objective called. Totally unaware of the connoted Cambodian wish for French protection, Montigny assigned a young French priest Hertrest^[5] to bring his draft treaty for Ang Duong to sign at Oudong, while Montigny himself left Cambodia with Bishop Miche to Vietnam.

The French priest Hertrest presented Montigny's draft treaty to King Ang Duong at Oudong in an audience with the presence of the pro-Siamese Battambang officials, who closely monitored Ang Duong's interactions with the French. Montigny's draft treaty only contained the commercial and religious issues and said nothing about French protection over Cambodia. Ang Duong rejected this treaty, which served him no purposes other than exposing his secret endeavors with France to Siam.^[5] Siam thus successfully prevented Cambodia from establishing relations with France for a time being.^[5]

Collier, with his corvette Capricieuse, joined his colleague Le Lieur at Danang in late October 1856.^[4]: 188 Both Collier and Le Lieur attempted to present diplomatic letter to Vietnam again but to no avail. The outbreak of the Second Opium War in October 1856 compelled both Collier and Le Lieur to take their respective corvettes Capricieuse and Catinat to leave Vietnam for China. The Vietnamese Emperor Tự Đức claimed this 'victory' over the French invaders. Due to the strong opposing northwestern monsoon winds, Montigny, from Cambodia, was obliged to take a circumventing detour, having to go through the coast of Borneo to Manila in the Philippines in order to reach Danang. Montigny and Bishop Miche eventually arrived in Danang in January 1857,^[4]: 188 three months after the departure of Collier and Le Lieur. Montigny threatened the Vietnam with gunboat diplomacy. Emperor Tự Đức appointed Đào Trí^[7] as the Vietnamese plenipotentiary to negotiate with Montigny. The negotiations apparently failed as both Montigny and Đào Trí did not find a compromising ground. Unlike Siam, Vietnam was unwilling to sign an unequal treaty.

Originally, the Catholic mission in the Continental Southeast Asia had been under management of Portuguese Dominican and Franciscan priests.^[8][9] The Catholic Church had been relying on Spain and Portugal for evangelization of the faraway lands. The Portuguese were granted exclusive authority over missionary activities in Asia under the Padroado system. However, the Portuguese missionaries had been struggling, with little success in preaching the Gospel and ended up just mostly maintaining the church for the Portuguese and Luso-Asian Mestizos in Southeast Asia. By the seventeenth century, the popes began to see the Padroado system as ineffective and sought to bring missionary works in Asia back to papal power.^[9] Congregation for the Propagation of Faith or Propaganda Fide was established in 1622^[9] under direct papal authority to oversee evangelization of peoples.

Advent of fruitful proselytization in Continental Southeast Asia began in Vietnam. By the seventeenth century, the Le-dynasty emperors ruled at the imperial capital of Thăng Long (modern Hanoi) only as puppets of the Trinh Lords, who only had power over Northern Vietnam, whereas Central Vietnam (called Cochinchina at the time) had been under the independent Nguyen Lords^[10] (Southern Vietnam was still part of Cambodia). Portuguese Jesuit priests from Macau began effective evangelization in Vietnam, starting in Cochinchina in 1615. However, like in China, Christianity readily conflicted with Confucianism, which put high emphasis on the ancestor worship.^[10] The Vietnamese called Christianity Hoa Lang đạo^[10] (花郎道, "Holland Religion"). Catholic missionaries instructed Vietnamese converts to destroy their ancestral shrines and ancestral tablets.^[10] Rejecting or refraining from ancestor worship constituted a serious crime that could be punished with death penalty according to Vietnamese law.^[10] The Nguyen Lords of Cochinchina issued bans and expelled the Jesuit priests in 1629 and 1649.

French Jesuit priest Alexandre de Rhodes arrived in Tonkin (Northern Vietnam) in 1627 from Macau but was soon expelled by the Trinh Lord in 1630. Ten years later, Alexandre de Rhodes came to proselytize in Cochinchina. In the span of five years, from 1640 to 1645, Alexandre de Rhodes was expelled by the Nguyen Lord four times,^[10] of which, at the last expulsion in 1645, De Rhodes was inflicted with death penalty but his sentence was commuted by the Nguyen Lord to exile.^[10] Meanwhile, in Northern Vietnam, the Trinh Lord issued bans on Christianity in 1649 and 1658. Vietnamese Catholics began to be persecuted and executed. However, in spite of the persecutions, the number of Vietnamese Catholics grew steadily to be at 80,000 in Tonkin and 20,000 in Cochinchina. Alexandre de Rhodes saw that if the Catholic Church were to establish a foothold in Asia, more missionaries were needed to be deployed and native priests should be trained. De Rhodes made his proposal to Pope Innocent X, who was pressured by Portugal,^[11] who claimed ancient rights accorded to them by the past popes, not to challenge Portuguese monopoly on missionary works in Asia.

Unsuccessful at his proposal to the pope, Alexandre de Rhodes turned to the French royal court of King Louis XIV. The French elites supported the idea of sending French priests to evangelize in Asia, leading to the establishment of Paris Foreign Missions Society (French: Société des Missions Etrangères de Paris, MEP) in 1658. De Rhodes recruited French secular priests François Pallu and Pierre Lambert de la Motte. In 1659, Pope Alexander VII consecreted François Pallu as the Apostolic Vicar of Tonkin and Lambert de la Motte as the Apostolic Vicar of Cochin. Bishop De la Motte left France in 1660, arriving in the Siamese royal capital of Ayutthaya in 1662^[11] and preparing to go to Vietnam. However, the Portuguese Jesuits priests in Cochinchina warned De la Motte of imminent persecution by the Nguyen Lord so De la Motte decided to stay in Ayutthaya for a time being. Bishop Pallu, along with another French priest Louis Laneau, left France in 1662, arriving in Ayutthaya in 1664.^[12]

Establishment of French Catholic mission in Continental Southeast Asia allowed France to pursue political and commercial interests in that region. French East India Company (French: Compagnie des Indes Orientales, CIO) was founded in 1664. At Ayutthaya, Bishop François Pallu the Apostolic Vicar of Tonkin and Bishop Lambert de la Motte the Apostolic Vicar of Cochinchina resided in Bangplahet, a Vietnamese^[12] community on the southeastern side of the city moat of Ayutthaya. Unable to go to Vietnam due to the ongoing persecutions, the two French bishops also faced resistance from the existing Portuguese clerics in the area, who refused to acknowledge authorities of the French bishops. In 1665, King Narai of Ayutthaya granted the land of Bangplahet for Pallu and De la Motte to build the Seminary of Saint Joseph as a school to train native priests. The Saint Joseph Seminary in Ayutthaya would serve as the base for French missionary activities in Vietnam.

Bishop De la Motte found that Siam was a tolerant kingdom, where Christians could practice religion and build churches without persecutions. The Siamese king Narai also found France to be a promising new incoming Western nation for Siam to counter the influences of the Dutch, who had been just imposed a naval blockade on Ayutthaya in 1663–1664,^[14] resulting in the humiliating Dutch–Siamese Treaty of 1664. De la Motte reported to the French court that King Narai was interested in Christianity and could be possibly converted.^[15] In 1665, Bishop Pallu returned to Rome from Siam to seek papal support against Portuguese resistance.^[12] Next year, in 1666, Bishop De la Motte at Ayutthaya sent out French MEP priests to evangelize;

• François Deydier went to preach in Tonkin or Northern Vietnam, settling in Phố Hiến in the Red River Delta.
• Louis Chevreuil went to preach in Cambodia, going through the Mekong Delta to settle in Phnom Penh.^[16]

In 1669, Bishop De la Motte, from Ayutthaya, went on a tour to visit Catholic communities in Vietnam. De la Motte brought Father Jacques de Bourges to settle in Phố Hiến in Tonkin to preach alongside Father Deydier. De la Motte also assigned Father Guillaume Mahot to proselytize at Hội An in Central Vietnam. After the tour, Bishop De la Motte returned to Ayutthaya. Also in 1669, Pope Clement IX created the Apostolic vicariate of Siam^[17] to be under exclusive jurisdiction of the French MEP order and assigned Bishop François Pallu to bring papal letter to the Siamese king. In 1670, Bishop Pallu asked the French king Louis XIV to write letters to the Siamese king and to the Vietnamese Emperor.

In 1670, Manuel de Oliveira Aragua^[15] a Cambodian–Portugese Mestizo captain in Cambodia arrested the French priest Louis Chevreuil for visiting Asia without Portuguese approval and allegedly for heresy.^[16] Chevreuil was sent to Macau and was then proceeded to the Inquisition at Goa. Pope Clement IX condemned the Portuguese arrest of Father Chevreuil, who was then released in 1672 to return to Siam. Bishop Pallu returned to Ayutthaya in 1673, where he presented the papal and French royal letters to the Siamese king Narai.^[14] Pope Clement also appointed Father Louis Laneau in Ayutthaya as the first Apostolic Vicar of Siam in 1674.^[17]

In 1674, Bishop François Pallu, from Ayutthaya, boarded on a French CIO ship to deliver French gifts to the Vietnamese Emperor at Hanoi. However, the ship was attacked by the Dutch and ended up shipwrecked in Manila in the Philippines. Spanish authorities arrested Bishop Pallu, who was sent to Madrid for trial.^[12]

Even though the Nguyen Lord Nguyễn Phúc Tần had earlier persecuted Christians and had expelled the Jesuits, the Nguyen Lord saw the French newcomers as commercial opportunities. Nguyễn Phúc Tần welcomed Father Guillaume Mahot to reside in Cochinchina and wrote to the Siamese king Narai to allow Bishop De la Motte to move to Cochinchina.^[14] King Narai, however, refused to let go of De la Motte as he wanted to keep De la Motte as the intermediary in Franco–Siamese diplomatic ventures.^[14] Nevertheless, Father Mahot brought a ship from Cochinchina to bring Bishop De la Motte to Cochinchina. Bishop De la Motte reached Huế in 1676, where he was welcomed by the Nguyen Lord. However, De la Motte eventually decided to return to Ayutthaya.

Both Pope Innocent XI and King Louis XIV secured the release of Bishop François Pallu from Madrid in 1677.^[12] Bishop Lambert de la Motte died at Ayutthaya in 1679. Pope Innocent then reorganized the vicariate administration in Vietnam;

• Guillaume Mahot of MEP succeeded De la Motte as the new Apostolic Vicar of Cochinchina
• Apostolic vicariate of Tonkin or Northern Vietnam, which contained a large number of Vietnamese Catholics, was divided into two new vicariates;
  • Apostolic vicariate of Western Tonkin, with Jacques de Bourges of MEP as the first Apostolic Vicar of Western Tonkin, based at Phố Hiến
  • Apostolic vicariate of Eastern Tonkin, with François Deydier of MEP as the first Apostolic Vicar of Eastern Tonkin, based at Kẻ Sặt

In 1668, the French East India Company settled in Surat, which later became French India. In 1670, François Baron the French commissioner at Surat sent delegates of the French East India Company to establish commercial relations with Siam and Vietnam;

• André Boureau-Deslandes, with the ship Vautour, visited Ayutthaya to establish commercial relation with Siam.^[18]: 78 This was the first official diplomatic contact between France and Siam. King Narai allowed the French to establish a comptoir or trade factory in Ayutthaya.
• A French merchant named Chapelain, travelling with the ship Tonkin, went to Thăng Long (Hanoi) to establish commercial relation with Tonkin.^[19] Chapelain had an audience with the Vietnamese Emperor Lê Hy Tông. The Trinh Lord Trịnh Tạc allowed the French to establish a comptoir at Phố Hiến.

The French bought a large amount of merchandises from Tonkin, carrying on a French ship Soleil d'Orient from Tonkin to Ayutthaya. The Siamese king Narai, hoping to secure a relation with France, sent the Siamese Deputy Trade and Foreign Minister Okya Phiphatkosa to board on Soleil d'Orient to France in a diplomatic mission. Soleil d'Orient left Ayutthaya in 1681. However, Soleil d'Orient shipwrecked off the coast of Madagascar with all the crews, including the Siamese envoy, presumed dead. The Tonkinese merchandises on the ship were also lost at sea.

After his release from Madrid, Bishop François Pallu was appointed as the Apostolic Vicar of Fujian. Bishop Pallu returned to Ayutthaya with the ship Saint-Joseph. Saint-Joseph then took a French MEP priest François Lefebvre from Ayutthaya to Thăng Long in 1682 to ask for freedom of Christian preaching from the Trinh Lord, who refused.^[19] Bishop Pallu left Ayutthaya in 1683, reaching Zhangzhou in 1684 but Bishop Pallu died in Fujian in the same year.^[12] Chapelain remained as the French representative in Phố Hiến until his death in 1686.^[19] Franco–Vietnamese relations in the seventeenth century would not be as prolific as the Siamese counterpart.

Constantine Phaulkon, a Greek adventurer and a former employee of English East India Company, arose to the position of Prime Minister of Siam at the death of Kosa Lek in 1683. In 1684, King Narai sent second Siamese diplomatic mission to France, led by two Siamese officials Okkhun Phichaiwanit and Okkhun Phichit Maitri,^[20] after the failure of the first mission, under guidance of a French MEP priest Bénigne Vachet, who led the Siamese envoys to Paris. The two Siamese envoys had an audience with the French King Louis XIV at the Palace of Versailles. Louis XIV reciprocated by sending Chevalier de Chaumont to lead a French diplomatic mission to Siam in 1685, leading to the conclusion of the Franco–Siamese Treaty of 1685,^[3]: 29 signed at King Narai's Palace at Lopburi, allowing the French missionaries to preach freely in Siam, granting exemption of duties and tin export monopoly from Phuket to the French East India Company, also allowing the French to settle in Songkhla in Southern Siam. Phaulkon then conspired with the French Jesuit priest Guy Tachard to bring the French to conquer Siam.^[21]

The French mission brought a large number of Vietnamese Catholics to study at the Saint Joseph Seminary in Ayutthaya. With papal support, the French MEP order practically supplanted the mostly-Portuguese Dominican, Franciscan and Jesuit priests as the main pioneer of evangelization in the region. There were still a substantial number of Portuguese priests in Siam and Vietnam, who refused to accept French priests as their overseers. As French–Portuguese rivalry over Catholic Church in Southeast Asia became more intense, Pope Innocent XI sought a compromise among the competing orders.^[10] Allowing the French MEP priests to monopolize missionary works in Asia would only result in schism so the Pope toned down dominance of the French. At the death of Bishop François Deydier of Eastern Tonkin in 1683, the Vicariate of Eastern Tonkin was given to Spanish Dominican Order. Also, with the death of Bishop Guillaume Mahot of Cochinchina in 1684, François Perez, a native priest with Filipino father and Siamese mother,^[13] who graduated from the Saint Joseph Seminary of Ayutthaya^[13] and did not belong to any orders, was made to succeed Mahot as the new Apostolic Vicar of Cochinchina in 1687.

In 1686, King Narai sent the third and most well-known mission under Kosa Pan, along with Jesuit priest Tachard, accompanying De Chaumont back to France. Tachard presented Phaulkon's plan to the French royal court, who began their own plan to conquer Siam. King Louis XIV sent second embassy under Simon de la Loubère, along with General Desfarges to bring around 600 French men to Siam. King Narai allowed Desfarges to station French troops in Bangkok, downstream from Ayutthaya and at Mergui on the Tenasserim Coast. La Loubère concluded the Franco–Siamese Treaty of 1687 with the Siamese signatory Okya Phrasadet the Phrakhlang or Siamese Foreign Minister. Most of the clauses of this new Treaty of 1687 was similar to the previous Treaty of 1685, with additional clauses allowing the French to settle and establish posts anywhere in Siam and allowing France to impose extraterritoriality on Siam.^[3]: 37 Véret arrived as the director of the French comptoir, technically the French headman and representative of the company in Siam.

King Narai allowing the French to exert influence over Siam upset native Siamese mandarins, who formed a nationalistic resistance movement under leadership of Okphra Phetracha,^[23]: 2 who accused Constantine Phaulkon and the French of planning to conquer Siam and to destroy Buddhism. In January 1688, King Narai sent his fourth mission to Europe led by Father Guy Tachard to bring Narai's amicable letters to the French king and the Pope.^[20] However, King Narai fell ill two months later in March 1688. Both Phaulkon and Phetracha vied for power. Without support of Desfarges from Bangkok, Phaulkon was overwhelmed by Phetracha, who seized King Narai's Palace in Lopburi and had Phaulkon executed in June.

Phetracha sent Siamese forces to attack and lay siege on Desfarges at the Bangkok fort. King Narai died in July 1688. Phetracha proclaimed himself new King of Siam, founding the Ban Phlu Luang dynasty^[23]: 2 that would rule Siam until the Fall of Ayutthaya in 1767. Kosa Pan the Siamese envoy to France in 1686 was appointed as Phrakhlang Foreign Minister under Phetracha. After five months of siege, Kosa Pan agreed to let Desfarges bring the French forces to leave Siam peacefully, with hostages exchanged to guarantee the terms.^[24]: 44 Bishop Louis Laneau the Apostolic Vicar of Siam also served as the guarantor of the terms.^[24]: 44 However, Desfarges broke the terms by taking the Siamese hostages, along with Véret, with him to Pondicherry.^[24]: 44

Kosa Pan the Siamese Foreign Minister punished Bishop Laneau and the French in Ayutthaya for Desfarges' breaking of the terms. Laneau, along with other French priests, merchants and Vietnamese seminarians, were all subjected to tortures and humiliations, some of them died in the process. Desfarges and Véret, seeking revenge on Siam, brought a French warship with 330 men to Junkceylon or Phuket in April 1689,^[25] calling for Kosa Pan to make a new treaty and to cede Phuket to France.^[25] The French in Phuket, however, did not manage to impose strong pressure on Siam. Desfarges eventually gave up and leave Phuket in November 1689,^[25] while also returning the Siamese hostages, ending the Franco–Siamese conflicts.

Guy Tachard, King Narai's envoy to Rome and Paris, was informed about the Siamese expulsion of the French and ascension of the new king Phetracha in November 1689,^[20]: 114 more than one year after the actual event. King Louis XIV assigned Father Tachard to return to Siam to bring a new French royal letter to Phetracha to restore Franco–Siamese relations and also to ask Siam to allow the French to settle in Mergui. Tachard reached Pondicherry in 1691. King Phetracha decided to restore relations with France so he released Bishop Laneau and other French subjects from prison, after thirteen months of incarceration.^[15]: 199 However, Tachard felt himself not ready to ask Siam to cede Mergui to France this time.

In 1693, during the Nine Years' War, the Dutch conquered Pondicherry. Guy Tachard was taken as captive to Holland and was later released. Unwavering, Tachard returned to Ayutthaya 1695 but was denied entry by Kosa Pan who said Tachard, arriving in a mere Portuguese merchant ship, lacked diplomatic credentials.^[20]: 68 Eventually, Tachard managed to acquire a warship from Pondicherry to enter Siam at Mergui in 1698. Tachard presented Louis XIV's letter from ten years ago in 1689 to King Phetracha in January 1699.^[20]: 76 However, Tachard did not have enough courage to ask Phetracha to cede Mergui. Phetracha's reply letter was only about blank ceremonial praises on the French king without any actual concessions the French had been hoping for.^[20]: 77

Bishop Louis Laneau the Apostolic Vicar of Siam died at Ayutthaya in 1697.^[17] Before his death, Bishop Laneau composed Encounter with Buddhist Sage (French: Rencontre avec un sage bouddhiste) as a Christian catechism that criticized Siamese Buddhism in favor of Christianity. In 1700, the new Nguyen Lord Nguyễn Phúc Chu persecuted the Portuguese-affiliated Catholics, leading to an exodus of Vietnamese Catholics from Cochinchina to Chanthaburi in Eastern Siam. In 1702, Bishop Louis Champion de Cicé arrived in Ayutthaya as the new Apostolic Vicar of Siam.^[17] In 1711, Bishop Cicé sent Father Huette to found the Immaculate Conception Church at Chanthaburi to accommodate Vietnamese Catholic refugees fleeing persecutions from their homeland.^[17]

Both the Trinh Lords of Northern Vietnam and the Nguyen Lords of Central Vietnam allowed the Catholic missionaries to reside only for commercial benefits accorded with them as presence of French priests attracted French trade activities. However, the Siamese expulsion of the French in 1688 greatly affected the state of French commerce in the region. In 1706, the French East India Company became insolvent.^[26] In 1709, the Company had to sell commercial privileges in Asia to the merchants of Saint-Malo.^[26] With the decline of French trade, the Vietnamese lords found no reasons to allow the French priests to continue to reside in Vietnam. Moreover, the Vietnamese lords also found the overwhelming number of the Vietnamese Catholics, who might listen to the missionaries rather than the Vietnamese lords, to be political threats and France might utilize religion to exert influence over Vietnam.

In 1712, the Trinh Lord Trịnh Cương of Tonkin or Northern Vietnam issued an edict banning Christianity. Any Tonkinese caught practicing Christianity would be tattooed học Hoa Lang đạo (學花郎道, "Study Holland Religion") in their faces.^[10] Next year, in 1713, Trịnh Cương expelled all the French Catholic priests from Tonkin. Three French priests in Tonkin; Bishop Jacques de Bourges the Apostolic Vicar of Western Tonkin, Father Edme Bélot and Father François-Gabriel Guisain, were forcibly boarded on a ship from Phố Hiến to leave Tonkin. Upon getting out of the Red River Delta, Father Bélot and Father Guisain sneaked back into Tonkin, establishing their new base in Nghệ An province. Bishop De Bourges took refuge in Ayutthaya, where he died next year in 1714. In 1719, the French East India Company was taken over by John Law's Company. In 1723, Trịnh Cương conducted another Catholic persecution in Tonkin, with the Tonkinese Christians punished and executed. Vietnamese persecutions sent waves of religious refugees to Chanthaburi and Ayutthaya.

In 1730, a young Chinese man in Ayutthaya named Laurent Teng,^[27] whose father was Chaophraya Phrakhlang Chin the deceased Siamese Trade Minister of Chinese descent and whose mother was a Vietnamese Catholic,^[27] who had been entrusted by his mother to be a Catholic at young age, was ordained as a Catholic priest, upsetting his Chinese paternal family, who sought assistance from Prince Phon of the Front Palace, younger brother of the reigning King Thaisa (grandson of Phetracha) of Siam. Prince Phon had Teng flogged with rattan canes and forced Teng to adorn himself in yellow Buddhist monk robes and to trample on a Christian cross.^[17] Prince Phon also discovered the Catholic catechism Encounter with Buddhist Sage, composed by the late Bishop Laneau, written in Siamese language using the sacred Khmer script, which could only be used to inscribe Buddhist religious texts, insulting Buddhism. King Thaisa then commissioned Phraya Phichairacha the Phrakhlang or Siamese Foreign Minister, also of Chinese descent,^[27] to conduct investigation.

Phicharacha the Phrakhlang Foreign Minister arrested Bishop Tessier de Quéralay the incumbent Apostolic Vicar of Siam and the rest of the French missionaries for the crime of blasphemy on Buddhism. Phicharacha told the French Catholic priests that using the sacred script to write condemnations on Buddhism was a great crime. King Thaisa issued a decree in January 1731 forbidding Catholic missionaries from preaching on native Siamese, Mon, Northern Thai and Lao people, not to 'lure' the said people into Christianity and not to condemn Buddhism.^[17][27] Phichairacha also had a stone stele inscribed with this new law to be placed in front of the Saint Joseph Seminary in Ayutthaya.^[27] Unlike Vietnam, Siam did not expel the French missionaries, allowing them to practice their religion but evangelization on the native peoples was prohibited.

In 1723, the French East India Company was retrieved and reorganized. By the eighteenth century, the Nguyen Lords had been expanding their dominions into Mekong Delta. French bishop Armand-François Lefebvre of MEP, the newly-appointed Apostolic Vicar of Cochinchina, began his episcopacy by preaching in Saigon in 1743.^[29] Pierre Poivre was a former MEP missionary in Cochinchina who turned to commerce, becoming a merchant. In 1749, François Dupleix the Governor-General of French India at Pondicherry sent Pierre Poivre as the delegate of the Company to procure a commercial relation with Cochinchina under Nguyen Lord Nguyễn Phúc Khoát. Nguyễn Phúc Khoát, however, did not agree, prompting Poivre to abduct a Vietnamese official who was the French translator,^[28] angering the Nguyen Lord. Next year, in 1750, Nguyễn Phúc Khoát expelled all French Catholic priests from Cochinchina. Bishop Lefebvre the Apostolic Vicar of Cochinchina had to flee from Huế to Macau, eventually settling in Prambeichhom, near the Cambodian royal capital of Oudong, in 1757, where he died in 1760.^[29] Bishop Guillaume Piguel succeeded Lefebvre as the new Apostolic Vicar of Cochinchina, not residing in Cochinchina but rather at Prambeichhom in Cambodia due to the persecution.

In 1765, King Hsinbyushin of Burma sent Burmese armies to lay siege on Ayutthaya. Pierre Brigot the Apostolic Vicar of Siam assigned Father Jean-Baptiste Artaud to bring Saint Joseph seminarians from Ayutthaya to take refuge at Chanthaburi. Father Artaud then brought the seminarians to found a new seminary at Hòn Đất^[30] in 1766 in the territory of the Principality of Hà Tiên. Bishop Piguel at Prambeichhom also sent Father Pierre Pigneau de Béhaine from Cambodia to teach at the Seminary of Hòn Đất.^[31] Prince Sisang, a refugee Siamese prince, at the suggestion of his Catholic followers,^[30] came to seek French aid with Father Artaud at Hòn Đất. Artaud, however, refused to meet with the Siamese prince for fear of political implications.^[30] Prince Sisang then proceeded to Prambeichhom, where Bishop Piguel introduced Sisang to take refuge under the King Ang Ton of Cambodia.

Ayutthaya fell to the Burmese invaders in April 1767,^[32]: 118 destroying the Siamese kingdom. The Seminary of Saint Joseph in Ayutthaya, built in 1665, was destroyed by the Burmese conquerors in 1767. Bishop Pierre Brigot the Apostolic Vicar of Siam was taken by the Burmese as captive to Rangoon in Lower Burma, where he stayed for some time and eventually went to Pondicherry without ever returning to Siam again. Mạc Thiên Tứ the ruler of Hà Tiên, wanting to keep Siamese refugee princes as political leverages against Taksin, the new King of Siam, was angered that Father Artaud let Prince Sisang go to Cambodia without informing him. Mạc Thiên Tứ arrested Father Artaud and Father Pigneau de Béhaine at Hòn Đất,^[30][31] who were imprisoned. Mạc Thiên Tứ then released both French priests on condition that Father Artaud would retrieve Prince Sisang to Hà Tiên. Father Artaud was obliged to go to Oudong in Cambodia, where Prince Sisang refused to return to Hà Tiên.^[30] In 1769, Cambodian-Chinese^[30] pirates attacked the Hòn Đất Seminary. Father Artaud died during the plunder,^[30] while Father Pigneau de Béhaine fled to Pondicherry^[31] as the seminary was destroyed. King Taksin of Siam then led Siamese forces to invade Cambodia and attack Hà Tiên in 1771 in search for Prince Sisang.

Father Jacques Corre, who had fled from Ayutthaya to Prambeichhom near Oudong, returned to Siam 1769 upon knowing that the Siamese had reestablished themselves at Thonburi under their new king Taksin.^[8] In 1770, King Taksin granted the land of Kudichin in Thonburi for Jacques Corre to build Santa Cruz Church to restore Catholic community in Siam.^[8] In 1772, Bishop Olivier-Simon Le Bon of MEP, coadjutor of Pierre Brigot the Apostolic Vicar of Siam captured by the Burmese, entered Siam along with his assistant Arnaud-Antoine Garnault to restore the Vicariate of Siam, staying at the Santa Cruz Church.^[17] When Father Corre died in 1773, Father Joseph-Louis Coudé arrived as replacement.

With the death of Bishop Piguel at Prambeichhom in 1771, Pigneau de Béhaine, who had been taking refuge in French India, was appointed to succeed Piguel as the new Apostolic Vicar of Cochinchina in 1774. Pigneau de Béhaine stayed in Hà Tiên rather than in Cambodia. In 1774, Bishop Le Bon did not allow Catholic officials in Siam to swear loyalty to the Siamese king in the traditional Hindu-Buddhist ceremony of drinking lustral water,^[17] preferring the Catholics to pay homage to the king in Christian rites,^[17] putting the French priests in direct conflict with King Taksin. Taksin arrested and imprisoned the three French priests Bishop Le Bon, Father Coudé and Father Garnault, putting them in cangues with chains on their necks, for nearly a year from September 1775 until their release in August 1776.

Tây Sơn uprising against the rule of the Nguyen Lords of Cochinchina in Central Vietnam began in 1771,^[33]: 366 led the three Tây Sơn brothers who also had Nguyễn family name. As the Tây Sơn toppled Nguyen rule and took control of Central Vietnam, members of the Nguyen Lord Nguyễn Phúc clan moved south to Saigon^[33]: 368 in Southern Vietnam. In 1777, Nguyễn Huệ, one of the Tây Sơn brothers, seized Saigon and massacred most of the Nguyễn Phúc clan,^[33]: 370 leaving only Nguyễn Phúc Ánh or Nguyễn Ánh as the sole surviving male member, who fled to Hà Tiên,^[33]: 370 where Nguyễn Phúc Ánh first met Bishop Pigneau de Béhaine. Nguyễn Ánh managed to return to retake Saigon from the Tây Sơn in the same year.^[33]: 370

In 1778, the Cambodians attacked Hà Tiên,^[31] compelling Bishop De Béhaine to move to Saigon, where De Béhaine became an acquintance of Nguyễn Ánh. In 1779, King Taksin was dissatisfied with insistence of the French Catholic priests in prohibiting the Siamese Catholic officials from participating in royal ceremonies so he expelled all the three French priests; Bishop Le Bon, Father Coudé and Father Garnault, from Siam.^[17] Bishop Le Bon went to Pondicherry where he died next year in 1780, while Coudé and Garnault went to Kedah.^[17] King Taksin was overthrown in 1782 and King Rama I ascended the throne, founding the Chakri dynasty.^[32]: 128

In 1783, the Tây Sơn again seized Saigon and took control of Southern Vietnam.^[33]: 374 This time, both Nguyễn Ánh and Pigneau de Béhaine had to make their separate journeys to take refuge in Bangkok, Siam. At Bangkok, De Béhaine (called Bá Đa Lộc^[33] in Vietnamese writings) offered to arrange for France to help Nguyễn Ánh to regain Vietnam. Nguyễn Ánh then entrusted Bishop De Béhaine with his state seal and his five-year-old eldest son Nguyễn Phúc Cảnh to go to France to ask for French assistance on the behalf of Nguyễn Ánh.^[33] Pigneau de Béhaine and Nguyễn Phúc Cảnh left Bangkok in December 1784. Meanwhile, King Rama I of Siam sent Siamese riparian fleet down the Mekong Delta to restore Nguyễn Ánh but was defeated by Nguyễn Huệ, the most prominent of the Tây Sơn brothers, in the Battle of Rạch Gầm-Xoài Mút^[33]: 375 in January 1785. De Béhaine reached Pondicherry in French India in February but his journey to France was stalled by uncooperative sentiments of the French authorities.^[31]

Bishop Coudé, who succeeded as the new Apostolic Vicar of Siam, arrived in Phuket from Kedah. The Siamese king Rama I invited Coudé to go to Bangkok. Bishop Coudé reached Bangkok in 1784,^[17] having an audience with the Siamese king. King Rama ruled that Siamese Catholic officials were not required to undergo the lustral-water drinking ceremony^[17] and allowed French missionaries to stay in Siam. However, Coudé faced strong resistance from the Portuguese–Siamese Mestizo Catholics, who had been resenting the French priests since the Ayutthaya period,^[17] who refused to attend any religious services conducted by Coudé,^[17] preferring a Portuguese priest from Macau. Coudé then decided to leave Bangkok for Kedah, of which he died on his journey at Takuathung in 1785.

After more than one year in Pondicherry, Bishop De Béhaine and Nguyễn Phúc Cảnh, then six years old, left Pondicherry in July 1786 for France, arriving at Lorient in Brittany in February 1787.^[31] De Béhaine took Nguyễn Phúc Cảnh to have an audience with King Louis XVI at the Palace of Versailles in May 1787, where De Béhaine pleaded for the cause of Nguyễn Ánh.^[31] The French royal court hesitated about sending military aid to an Asian potentate in a faraway land, as the French government before the French Revolution suffered fiscal problems. After six months, the French royal court finally consented to help Nguyễn Ánh. Treaty of offensive and defensive alliance concluded at Versailles on November 28, 1787, between France and Cochinchina (French: Traité d'alliance offensive et défensive conclu à Versailles, le 28 novembre 1787, entre la France et la Cochinchina),^[34]: 13 known colloquially in modern historiography as the Treaty of Versailles, was signed by Bishop Pigneau de Béhaine, the Apostolic Vicar of Cochinchina, on behalf of Nguyễn Phúc Ánh the King of Cochinchina, with ten articles;

• King Louis XVI of France promised to help Nguyễn Ánh in Article 1;

  Le Roi T. C. promet et s’engage de seconder de la manière la plus efficace les efforts que le Roi de la Cochinchine est résolu de faire pour rentrer dans la possession et jouissance de ses États.

  ^[34]: 14

  King of France promises and pledges to support in the most effective manner the efforts that the King of Cochinchina is resolved to make to regain possession and enjoyment of his States.

  by sending four frigates, 1,200 infantrymen, 200 artillerymen and 250 African soldiers in Article 2.^[34]: 14
• Nguyễn Ánh promised, in return, to cede the port of Danang or Tourane to France in Article 3;

  The King of Cochinchina, in anticipation of the important service that His Majesty King of France is willing to render him, cedes to him, as well as to the Crown of France, the absolute ownership and sovereignty of the island forming the principal port of Cochinchina called Hoi-Nan and by the Europeans Touron.

^[34]: 14 and to cede Pulo Condore (Côn Đảo) in Article 5;

King of France shall also have ownership and sovereignty of Pulo-Condor.

^[34]: 15

• France imposed trade monopoly on Cochinchina in Article 6, in which only the French, not any other Western nations, were allowed to trade freely in Cochinchina; "The subjects of King of France shall enjoy complete freedom of trade in all the states of the King of Cochinchina, to the exclusion of all other European nations.".^[34]: 15

Due to upheaval in Cambodia, Oknha Yomreach Baen, a Cambodian official, took the nine-year-old young king Ang Eng of Cambodia to take refuge in Bangkok under the Siamese king Rama I in 1782. Among many Cambodians who followed King Ang Eng to Bangkok was Keo Ribeiro,^[35] a Cambodian–Portuguese Mestizo Catholic man who entered the service under the Siamese king as Phra Wisetsongkhram the commander of Siamese artillery. King Rama appointed Oknha Yomreach Baen as Chaophraya Aphaiphubet as a regent to govern Cambodia on behalf of King Ang Eng, who lived in Bangkok as a refugee and political hostage.^[36]: 157

Nguyễn Phúc Ánh the last scion of the former Nguyen Lords took refuge in Bangkok in 1783, sending Bishop Pigneau de Béhaine as his delegate along with his son Nguyễn Phúc Cảnh to Paris to ask for French military aid in his struggle against the Tây Sơn. Bishop De Béhaine, on behalf of Nguyễn Ánh, concluded the Franco–Cochinchinese Treaty of Versailles of November 1787, in which France promised to help Nguyễn Ánh in exchange for Nguyễn Ánh ceding Danang and Côn Đảo to France. After conclusion of the Treaty, Bishop Pigneau de Béhaine and Nguyễn Phúc Cảnh returned to Pondicherry in French India in December 1788. However, the French royal government sent a confidential order^[28] to Thomas Conway the Governor of French India at Pondicherry to abrogate this treaty, refusing to actually help Nguyễn Ánh, for France could not financially support an unnecessary campaign in Asia under such state of fiscal problem.^[28] Thomas Conway refused to send French forces to aid Nguyễn Ánh as stipulated in the treaty. This 1787 Versailles Treaty thus became obsolete. Then, the French Revolution happened in 1789.

Nguyễn Huệ, the most prominent of the Tây Sơn brothers, marched north from Huế to successfully seize Thăng Long (modern Hanoi) in 1788,^[33]: 378 conquering Northern Vietnam, overthrowing the regime of Le-dynasty Emperor and the Trinh Lord and uniting the whole Vietnam from North, Center, to the South under one single rule of the Tây Sơn. Nguyễn Huệ declared himself Emperor Quang Trung during the repulsion of a Qing Chinese invasion in the Battle of Ngọc Hồi-Đống Đa in 1788. However, the two Tây Sơn brothers Nguyễn Nhạc the older brother, who was based at Quy Nhơn and Nguyễn Huệ the younger brother, who was based at Huế, came into an armed conflict, weakening the Tây Sơn. Nguyễn Phúc Ánh, who had been residing in Bangkok for five years, took this opportunity to leave Bangkok in 1787 to renew his reconquest campaign against the Tây Sơn. Nguyễn Ánh successfully took Saigon in 1788^[33]: 381 and established his power base on the Mekong Delta of Southern Vietnam.

As France did not honor the treaty,^[33]: 384 Bishop Pigneau de Béhaine had to raise his own funds to recruit French adventurers and French naval deserters in India to aid Nguyễn Ánh in Cochinchina,^[33]: 384 to buy two merchant ships and armed them into warships^[33]: 384 including Jean-Baptiste Chaigneau^[33]: 385 who commanded the ship Long (龍, Dragon) and Philippe Vannier^[33]: 385 who commanded the ship Phụng (鳳, Phoenix). Bishop De Béhaine brought the French volunteer navy to Nguyễn Ánh at Saigon in 1789.^[33]: 385 Olivier de Puymanel the French engineer and deserter designed the Saigon citadel in Western Vauban model. Jean-Baptiste Chaigneau also trained Nguyễn Ánh's Cochinchinese forces in Western discipline. French contribution to Nguyễn Ánh's navy was crucial but should not be exaggerated as the French constituted only a minority in the Cochinchinese forces.^[33]: 384 Emperor Quang Trung Nguyễn Huệ of Tây Sơn died in 1792, succeeded by his son Nguyễn Quang Toản.^[33]: 380

In 1794, King Rama I of Siam allowed Ang Eng, who had been residing in Bangkok since 1782 for twelve years, to go to assume personal rule in Cambodia^[36] as King Noreay Reachea under Siamese domination. The Siamese king also partitioned Northwestern Cambodia, including the srok of Battambang and Siemreap, for Chaophraya Aphaiphubet to govern under direct Siamese administration,^[36] not subjected to the King of Cambodia at Oudong, as a reward for Aphaiphubet's devotion to promote Siamese influence in Cambodia. King Noreay Reachea Ang Eng of Cambodia only ruled personally for three years until his premature death from illness at the age of twenty-four in 1797.

Nguyễn Phúc Ánh utilized monsoon winds to propel his fleet northward in his reconquest campaign.^[33]: 386 Bishop Pigneau de Béhaine took Nguyễn Ánh's son Nguyễn Phúc Cảnh to the battles. Bishop De Béhaine refused to baptize Nguyễn Phúc Cảnh for fear of retributive reaction from Nguyễn Ánh's circle^[31] but Nguyễn Phúc Cảnh had already acted as if he were a Christian, refusing to worship his ancestors.^[33]: 387 In 1799, Nguyễn Phúc Ánh led his fleet to attack Quy Nhơn in Central Vietnam. Pigneau de Béhaine died in October 1799^[31] from illness during this siege of Quy Nhơn. Both Nguyễn Phúc Ánh and his son Nguyễn Phúc Cảnh deeply mourned^[31] the death of Bishop Pigneau de Béhaine, who had brought French assistance to Nguyễn Ánh.

After his conquest of Quy Nhơn, Nguyễn Phúc Ánh quickly proceeded northward to successfully take Huế in 1801. However, Nguyễn Phúc Cảnh, the Christian-professing eldest son of Nguyễn Ánh, died from illness, also in 1801. At Huế, Nguyễn Phúc Ánh proclaimed himself Emperor Gia Long in 1802, founding the Nguyen dynasty.^[33]: 395 Gia Long marched north to seize Thăng Long (Hanoi) in 1802,^[33]: 395 taking control of Northern Vietnam, uniting the whole country of Vietnam from North to South and ending the Tây Sơn dynasty. Bishop Jacques Longer the Apostolic Vicar of Western Tonkin, based at Kẻ Vĩnh in Ninh Bình province, came to visit Gia Long in Hanoi, asking for guarantee of Catholic freedom of worship and Gospel preaching, to which Gia Long did not answer. Gia Long took Nguyễn Quang Toản the last Tây Sơn Emperor from Thăng Long to be executed at Huế. Bishop Jean Labartette, who succeeded De Béhaine as the new Apostolic Vicar of Cochinchina, came to ask Gia Long in 1803 for freedom of Christians, to which Gia Long also did not promise.

In 1806, the Siamese King Rama I enthroned Ang Chan, eldest son of the deceased king Ang Eng, as the new King Outey Thireach Reamea of Cambodia, again under Siamese auspices.^{[5]: 6 [33]: 409} Weary of Siamese influences over Cambodia, King Ang Chan turned to the Vietnamese Emperor Gia Long. In 1812, Ang Chan's younger brother Ang Snguon, who as pro-Siam, rebelled against Ang Chan.^[5]: 35 Siam sent forces into Cambodia to support Ang Snguon,^[5]: 35 prompting Ang Chan to flee from Oudong the royal capital of Cambodia to take refuge at Saigon in Southern Vietnam under protection of Gia Long.^{[5]: 37 [33]: 410} Ang Chan's two other younger half-brothers, the Princes Ang Em and Ang Duong, also decided to join Siam. The Siamese forces burnt down the Cambodian royal city of Oudong and returned, with the pro-Siam Cambodian princes Ang Snguon, Ang Em and Ang Duong, younger brothers of Ang Chan, going with the Siamese to Bangkok. Emperor Gia Long appointed Lê Văn Duyệt as Tổng trấn Thành Gia Định (總鎮城嘉定) or the Viceroy of Saigon to march the Vietnamese forces to bring Ang Chan from Saigon to be restored in Cambodia in 1813.^{[5]: 37 [33]: 410} Lê Văn Duyệt built the Banteay Keav citadel at Phnom Penh as the new royal seat for Ang Chan. Ang Chan, with Vietnamese support, resumed his rule in Cambodia, with Cambodia shifted from Siamese to Vietnamese domination.

Even though Emperor Gia Long was a Confucian, he did not persecute the Christians in Vietnam because the emperor had to make use of French men in his reign,^[37] just tolerating Christianity but not embracing it either. French adventurers Jean-Baptiste Chaigneau and Philippe Vannier continued to serve in Vietnam as Gia Long's officials. The prospect of having a Christian king in Vietnam, however, died with the death of his Christian-sympathetic eldest son in 1801.^[37] Gia Long accorded Lê Văn Duyệt, his comrade during the Tây Sơn Wars, with extensive autonomous powers as the Viceroy of Saigon in Southern Vietnam. Even though the Vietnamese imperial court began to distrust the missionaries,^[38] when Gia Long died in 1820, there were up to 300,000 Catholics in Northern Vietnam and 60,000 Catholics in Central and Southern Vietnam combined, becoming a visible minority. Gia Long's other son ascended the Vietnamese throne as Emperor Minh Mạng, who had a staunchly Confucian and anti-Western view.

Jean-Baptiste Chaigneau, after his thirty years of service in Vietnam, went to France in 1819 during the Bourbon Restoration period. The French royal government of King Louis XVIII found Chaigneau's connection to Vietnam an opportunity to establish a trade relation with Vietnam. Jean-Baptiste Chaigneau was appointed as the French Consul to Vietnam. However, when Chaigneau returned to Vietnam in 1821, Gia Long had already died^[28]: 16 and the new emperor Minh Mạng was very antipathic towards Christians and Westerners. Minh Mạng declined Chaigneau's proposal to establish a commercial relation and did not accept Chaigneau as the Consul.^[28]: 16 With the Vietnamese imperial court turned cold towards Westerners, both Jean-Baptiste Chaigneau and Philippe Vannier resigned, packed up and left Vietnam permanently in 1824,^[33] never returning.

In February 1825, Emperor Minh Mạng issued a ban on Christianity,^[33]: 422 declaring that Christianity was a heterodox religion that had no respect for Buddha and ancestors^[33]: 421 (Buddhism and Confucianism), shaking the very foundation of Vietnam's social order and forbade any Westerners from ever entering Vietnam.^[33]: 422 Port officials were to search all incoming foreign ships for any Western missionaries who would sneak into Vietnam. Minh Mạng also called for all of existing missionaries in Vietnam to come to Huế under pretext of working as translators to the emperor^[38] but Minh Mạng intended to detain all the missionaries under his watch to prevent them from preaching. The power of the new emperor seemed not to extend to Southern Vietnam, where Lê Văn Duyệt protected the missionaries.^{[33]: 421 [38]} France sent Eugène Chaigneau, nephew of Jean-Baptiste Chaigneau, to Vietnam again in 1826 but Minh Mạng did not welcome him.^[28] In 1828, Lê Văn Duyệt went from Saigon to Huế to urge Minh Mạng to release the missionaries.^[38] Even the emperor complied to the powerful Lê Văn Duyệt as Minh Mạng was obliged to release the missionaries.

Death of Lê Văn Duyệt in 1832 left no powerful figure to protect the Christians, leading to full-scale Christian persecution under Minh Mạng. In January 1833, Minh Mạng issued a more severe edict of Christian ban. All Vietnamese Christians were required to immediately leave Christianity and they had to prove themselves by trampling on the Christian cross or else they would face punishments. All Christian churches in Vietnam were to be destroyed. This persecution compelled all French and Spanish Catholic missionaries in Vietnam to go into hiding. Jean-Louis Taberd the Apostolic Vicar of Cochinchina and his assistant Father Étienne Cuenot fled from Saigon to Bangkok, where the Siamese king Rama III welcomed them. Another French MEP priest François-Isidore Gagelin in Southern Vietnam was arrested and executed.^[1] In the same year, Lê Văn Khôi, adopted son of the deceased Lê Văn Duyệt, arose in rebellion against Minh Mạng. Majority of the Vietnamese Catholics in Southern Vietnam joined his rebellion.^[33]: 421 The Lê Văn Khôi rebels took control of all the Six Provinces of Southern Vietnam,^[33]: 426 establishing their base at the Saigon citadel. Minh Mạng responded by dispatching his own military forces to suppress the rebellion.

With ongoing rebellion in Southern Vietnam, the Siamese king Rama III or King Nangklao saw an opportunity to reclaim control over Cambodia and to even push into Southern Vietnam. In November 1833, King Nangklao sent Chaophraya Bodindecha to lead the Siamese land armies to invade Cambodia by land and Chaophraya Phrakhlang Dit Bunnag to lead the Siamese navy to strike at Hà Tiên. The Siamese king ordered the French bishop Jean-Louis Taberd to join the Siamese armies in the campaign. Taberd and his colleague Cuenot instead moved to Singapore. After taking control of Cambodia and Hà Tiên, the Siamese land army under Bodindecha and Siamese navy under Phrakhlang Dit Bunnag joined forces to proceed down the Mekong Delta towards Saigon. Minh Mạng's forces, who had been beseiging the rebel-held Saigon, had to allocate forces under Trương Minh Giảng to face the invading Siamese. Trương Minh Giảng defeated the Siamese in the Battle of Vàm Nao on the Mekong in January 1834, prompting the Siamese to retreat. Phra Wisetsongkhram Bento Ribeiro de Albergaria,^[35] who inherited his title and position from his grandfather Keo Ribeiro, a Cambodian–Portuguese Mestizo artilleryman under Siamese service, led the Vietnamese Catholics of An Giang province to move to Bangkok, where they were settled in Samsen.

As the Siamese had retreated, King Nangklao set up the Cambodian prince Ang Em as the governor of Battambang^[5]: 57 in the Siam-controlled Northwestern Cambodia. The pro-Vietnam King Ang Chan of Cambodia died in 1835 without male heirs. Trương Minh Giảng the Vietnamese resident in Cambodia took this opportunity to exert his influence as Minh Mạng put up a young Cambodian princess Ang Mey, daughter of Ang Chan, as a puppet Queen Regnant of Cambodia at Phnom Penh under Vietnamese influences.^{[5]: 59 [33]: 429} Minh Mạng's forces also took Saigon in 1835, putting the end to the rebellion. Joseph Marchand, a French MEP missionary, was found by Minh Mạng's forces among the rebels, became implicated and was executed by slow-slicing in November 1835. In late 1835, Minh Mạng established the Trấn Tây province over Cambodia to impose direct Vietnamese rule and appointed Trương Minh Giảng as Trấn Tây tướng quân (鎮西將軍) or the Governer-General of Cambodia.^[5]: 61

In the aftermath of the Lê Văn Khôi Rebellion, Minh Mạng's persecutions of missionaries only increased in intensity. In 1836, Bishop Jean-Louis Taberd appointed Étienne Cuenot as his coadjutor and sent Cuenot to Vietnam for survey. Cuenot found a safe spot in Gò Thị near modern Quy Nhơn. Jean-Charles Cornay, a French Catholic priest preaching in Northern Vietnam, was arrested in 1837 and was executed by decapitation, amputation of limbs and dissection of his body.^[39] Joseph Havard the Apostolic Vicar of Western Tonkin died from illness in 1838 during his hiding from Vietnamese authorities. Pope Gregory XVI appointed Pierre Dumoulin-Borie as the new Apostolic Vicar of Western Tonkin but Father Borie was executed before the papal order reached him in Northern Vietnam. Two French MEP missionaries; François Jaccard and Gilles Delamotte, were executed by the Vietnamese in Quảng Trị province in 1838 and 1840, respectively.^[1]

Bishop Jean-Louis Taberd, who had taken refuge in Singapore, sent two MEP priests Jean-Claude Miche and Pierre Duclos to preach in Siam-controlled Battambang in Northwestern Cambodia in 1838. Taberd was then appointed as Apostolic Vicar of Bengal and moved to Calcutta in British India and Pope Gregory XVI appointed new Apostolic Vicars to Vietnam;

• Étienne Cuenot at Gò Thị in Central Vietnam was appointed to succeed Taberd as the new Apostolic Vicar of Cochinchina.^[40]
• Pierre-André Retord of MEP in Sơn Tây was appointed as the new Apostolic Vicar of Western Tonkin.

In 1839, Pope Gregory issued papal brief Quod nuncia^[40] praising the Catholics of Vietnam for their endurance of persecutions by the Vietnamese imperial court. In mid-1839, a conflict broke out between the British Empire and Qing-dynasty China, resulting in the First Opium War. Upon learning about the British prevail over China, Emperor Minh Mạng of Vietnam realized military prowess and potential threats of Westerners, prompting the Vietnamese Emperor to seek an amicable relation with France.^[28] In late 1839, Minh Mạng dispatched two Vietnamese envoys Trần Viết Xương and Tôn Thất Thường in a diplomatic mission to France.

Also in December 1839, the Cambodian prince Ang Em, who had been set up by the Siamese as the governor of Battambang, rebelled against Siam and went to Phnom Penh to defect to Trương Minh Giảng the Vietnamese commissioner of Trấn Tây province.^[5]: 68 Due to this upheaval in Battambang, Father Miche and Father Duclos moved from Battambang to Penang to take refuge. In mid-1840, Emperor Minh Mạng dethroned Ang Mey the puppet Queen of Cambodia in his effort to annex Cambodia into Vietnam,^[41]: 158 exiling her to Saigon. Dissatisfied with Vietnamese cultural assimilation policies, the Cambodians arose in a nationwide uprising against Vietnamese rule in September 1840.^[41]: 157 The Siamese armies under Chaophraya Bodindecha took this opportunity to intervene by supporting this Cambodian uprising against Vietnam.^[5]: 76

The two Vietnamese envoys, Trần Viết Xương and Tôn Thất Thường, reached Brest in Brittany in November 1840^[28]: 32 and then proceeded to Paris. France was then under the July Monarchy of King Louis-Philippe of the Orléans dynasty. This Vietnamese mission, drawing sensation in Paris, proposed a commercial relation with France. However, the Paris Foreign Missions Society took this opportunity to relay grievances against Vietnam's violent persecutions of the French missionaries and Vietnamese Catholics to the French government.^[28]: 32 Pope Gregory XVI himself also pleaded the French king Louis-Phillippe to use French military power to put the end to Vietnam's Catholic persecutions.^[28]: 32 Pressured by the Catholic Church, King Louis-Phillippe refused to receive the Vietnamese envoys.^[28]: 32 The Vietnamese envoys then left France empty-handed. The Protestant French Foreign Minister François Guizot declared that France was not responsible for actions and safety of French missionaries in Asia, saying that the missionaries had brought themselves into the risks.^[28]: 32 French public opinion, however, was sympathetic to the missionaries and supportive of French intervention on behalf of the French missionaries in Asia.

Emperor Minh Mạng died in January 1841, succeeded by his son the new emperor Thiệu Trị. The Siamese under Bodindecha installed Ang Duong the Cambodian prince as their own candidate in Oudong against the Vietnamese.^[5]: 81 Under the new Vietnamese Emperor, more French missionaries sneaked into Vietnam and were arrested;

• Two French priests Jean-Paul Galy-Carles and Siméon Berneux, from Macau, entered Northern Vietnam and were arrested in Kim Sơn, Ninh Bình province.
• French priest Pierre Charrier was arrested in Sơn Tây to the northwest of Hanoi.
• Jean-Claude Miche and Pierre Duclos joined Bishop Cuenot the Apostolic Vicar of Cochinchina at Gò Thị in Central Vietnam.

In September 1841, Pope Gregory issued the papal brief Universi Dominici^[42] dividing the Apostolic Vicariate of Siam into Apostolic Vicariate of Western Siam based at Singapore and Apostolic Vicariate of Eastern Siam based at Assumption Church in Bangkok. Jean-Baptiste Pallegoix the Bishop of Mallus was appointed as the first Apostolic Vicar of Eastern Siam in this new division.

Facing strong Cambodian resistance with Siamese support, the Vietnamese were obliged to evacuate from Cambodia in November 1841, ending the period of direct Vietnamese rule over Cambodia as Trấn Tây province, with Trương Minh Giảng the Vietnamese Commissioner of Cambodia allegedly committed suicide.^[5]: 92 Siam was able to resume control over Cambodia. In early 1842, the Siamese king Rama III or King Nangklao assigned his younger half-brother Prince Itsaret Rangsan, along with Chuang Bunnag, to lead the Siamese navy to attack Hà Tiên. The Siamese navy temporarily took position at Vietnam's Phú Quốc Island as they proceeded to attack Hà Tiên. However, the Siamese naval attack on Hà Tiên was repelled by the Vietnamese and the Siamese retreated. Also in early 1842, Bishop Cuenot at Gò Thị sent Father Miche and Father Duclos to proselytize on the Montagnard people including the Jarai people, Rade people and the Mnong people on the Central Vietnamese Highlands. However, Father Miche and Duclos were arrested by the Vietnamese authorities before reaching their destination.

Five French MEP priests; Jean-Paul Galy-Carles, Siméon Berneux, Pierre Charrier, Jean-Claude Miche and Pierre Duclos, were incarcerated in Huế, where they were beaten with rattan canes in judiciary procedures. In 1842, the Vietnamese Emperor Thiệu Trị sentenced all of the five French missionaries to death. Unlike his father Minh Mạng, however, Thiệu Trị was more cautious in dealing with the missionaries. Thiệu Trị reprieved the death sentences of the five priests. In fact, not a single Western missionary was executed during Thiệu Trị's reign, in contrast with his father Minh Mạng and his son Tự Đức. Meanwhile, there happened to be a French frigate Héroïne patrolling in the China Sea. Napoléon Libois the prosecutor of the Paris Foreign Mission in Macau, informed about the imprisonment of five MEP priests in Vietnam, asked capitaine de corvette Félix Favin-Lévêque the commander of Héroïne to rescue the missionaries.

Without consulting the French government, acting on his own initiative, capitaine de corvette Félix Favin-Lévêque (Y Lê Viết Ca)^[43] brought Héroïne to Danang in February 1843,^[1] threatening the Vietnamese imperial court to release the five missionaries or Favin-Lévêque would anchor at Huế Imperial Palace. Ngụy Khắc Tuần,^[43] a local official in Quảng Nam province, however, told Emperor Thiệu Trị that France had sent someone to apologize for the crimes of the French missionaries and ask to take them back. Out of mercy, Thiệu Trị granted to allow the five French MEP priests to leave Vietnam with Favin-Lévêque on Héroïne in March 1843 on condition that they would never return to Vietnam again. Even though no armed clashes happened, the expedition of Favin-Lévêque to Danang in early 1843 was the first of five successive French expeditions to Danang (1843, 1845, 1847, 1856 and 1858) to intervene on behalf of the missionaries, with some of them turned violent. As Favin-Lévêque managed to rescue all the five French priests to safety, dropping off Father Duclos at Singapore, Father Miche at Penang and others at Réunion. However, three of the five priests; Galy, Miche and Duclos, would soon return to Vietnam.

Charles de Montigny was born in 1805.^[44] Montigny's father used to serve Prince Comte de Provence, younger brother of King Louis XVI of France. During the French Revolution, as an émigré, Montigny's father took refuge in Hamburg in Germany,^[44] where Montigny was born. Only when Comte de Provence ascended the restored French throne as King Louis XVIII in 1814 that Montigny's family was able to return to France in 1815.^[44] At the age of eighteen, Montigny became a soldier and joined the French Invasion of Spain in 1823. Montigny then, without his family's approval, became a Philhellene, going to fight in the Greek War of Independence in 1827 under French commander Charles Nicolas Fabvier,^[44] who lauded Montigny's distinct bravery, rescuing another French commander from the encirclement of the enemies.^[44] Montigny continued his service under Fabvier for some time until he shifted his career to diplomacy, entering the Ministry of Marines.^[44]

British prevail over Qing China in the aftermath of the First Opium War made both Siam and Vietnam realized superior military prowess and potential threats of the incoming Westerners. British success in the Far East also urged France to find its own way to establish influence in Asia, emulating the British, not to be left behind. During the Sino–British negotiation of the Nanking Treaty, the French Foreign Minister François Guizot sent a French observatory mission to China, led by capitaine de vaisseau Jean-Baptiste Cécille,^[28]: 33 to Canton (Guangzhou) in order to explore potential diplomatic and commercial relations with China. In January 1842, in a confidential meeting, Yishan the Viceroy of Liangguang offered concessions and privileges to France in exchange for French support to China in conflicts with Britain,^[28]: 34 to which Jean-Baptiste Cécille replied that France could not act against Britain without a pretext.^[28]: 45 Nevertheless, the Chinese seemed to expect France to counter British influences.

In the aftermath of First Opium War, the British compelled the Qing imperial court to conclude the Treaty of Nanking (南京條約), to which Emperor Daoguang appointed Keying or Qiying, a member of the imperial Aisin-Goro clan, to be the chief negotiator and plenipotentiary. The Nanking Treaty was concluded in August 1842, which abolished the monopoly of Cohong merchants in Canton by allowing the British to trade freely in five mentioned ports and the British were also permitted to establish consulates in those five ports. As Keying arrived in Canton, he concluded Treaty of the Bogue (虎門條約) with the British in June 1843, which stipulated fixed duty rates for each individual trade articles (any articles not mentioned would be subjected to the general rule of five-percent import duty) and established British extraterritorial jurisdiction in the five ports.

In November 1843, François Guizot the French Foreign Minister assigned Théodose de Lagrené as the French plenipotentiary to conclude a treaty with China in similar manner to the British Treaty of Nanking.^[28] Montigny joined this diplomatic mission of Théodose de Lagrené to Asia^[44] in Montigny's first-time arrival in the region. The Lagrené Mission arrived in Macau in August 1844.^{[28]: 45 [45]} Keying, then Viceroy of Liangguang and chief negotiator of all treaties China was to make with Western nations, was the plenipotentiary and signatory on the Chinese part. The Treaty of Whampoa or Treaty of Huangpu^[45] (黃埔條約) was signed on 24 October 1844^[34]: 22 between China and France as an unequal treaty.^[45] The treaty terms included;

• Article 2 allowed the French to trade freely at five ports; Canton, Amoy, Fuzhou, Ningbo and Shanghai,^[34]: 23 in the same manner as the British.
• Article 4 allowed France to establish consulates in the five ports mentioned.^[34]: 23
• Article 6 stipulated fixed rates of import and export duties for each individual articles and China was forbidden to raise any duty rates fixed in this treaty.^[34]: 24 Any trading goods not mentioned would be subjected to the general rule of five-percent import duty (compare Siam's three-percent fixed import duty on all articles).
• This Whampoa Treaty did not directly stipulate the freedom of Christian proselytization. Article 22 only stated that France was allowed to build churches in the five ports.^[34]: 31
• Article 27 stipulated that, in case of conflict between a Chinese and a French, the Chinese authorities would arrest the Chinese subject to be put under Chinese judiciary system and the French consular authority would arrest the French subject to be judged according to the French law.^[34]: 33
• Article 28 stipulated that the Chinese authorities had no power to intervene in conflict between the French or between the French and another Western subject. The Chinese also had no power over French ships and French naval crew.^[34]: 33

Unlike the British, France had no commercial interests in China and strove to put forward religious issues to further France's role.^[45] Lagrené, at his own initiative and suggested by Keying himself, pushed for the legalization of Christianity in China.^[28]: 50 There were around 240,000 Christians in China at the time,^[46] mostly Catholics. In 1724, Emperor Yongzheng issued a general ban on Christianity in China and all the Western missionaries were ordered to gather in Canton.^[46] Western missionaries began to be executed. In 1811, Emperor Jiaqing conducted an eradication campaign on the remaining missionaries, who were executed.^[46] Keying supported Christian legalization as it would secure French support for China against Britain.^[28]: 55 Keying had to present many memorials to Emperor Daoguang, who conceded to lift all bans on Christianity in China in December 1844.^[28]: 56

Théodose de Lagrené, however, was not satisfied as he demanded the Qing imperial court to explicitly stipulate full toleration.^[28]: 61 In 1845, Lagrené, joined by Montigny, went on a tour to explore the five treaty ports. Lagrené complained to Keying that he had not seen a single poster announcing the legalization of Christians in the five ports he had visited.^[28]: 63 Lagrené acted with strong angry emotion and behavior towards Chinese officials, prompting Keying to report to Qing court that Lagrené "surpassed all other foreigners in arrogance and cunning".^[28]: 61 Keying convinced the Emperor to comply to the French demand because, if not, France would become another antagonistic nation towards China like Britain.^[28]: 64 Eventually, Daoguang issued an edict in February 1846^[28]: 64 permitting Chinese people to practice Christianity without being punished.^[34] However, Daoguang's legalization of Christianity was not honored by local Chinese officials, who continued to persecute Christians, leading to the French participation in the Second Opium War. The Lagrené Mission, which included Montigny, left China at Macau in January 1846^[28]: 64 to return to France.

The Sino–French Whampoa Treaty concluded by Théodose de Lagrené in 1844 marked the advent of grounded French presence in the Far East. French Naval Station in the China Seas (French: station navale des mers de Chine) was founded at Macau in 1844, to which capitaine de vaisseau Jean-Baptiste Cécille, who was promoted to Rear Admiral, was appointed as the commander. Also in 1844, French missionaries sneaked into Vietnam again;

• Jean-Claude Miche, one of the five priests who had just been rescued from Vietnam by the frigate Héroïne in 1843, returned to Vietnam, residing in Lái Thiêu near Saigon in Southern Vietnam.
• Dominique Lefebvre the Bishop of Isauropolis, coadjutor to Bishop Cuenot of Cochinchina, entered Vietnam to preach in Vĩnh Long province in Southern Vietnam.^[47]

Due to frequent persecutions of Western missionaries by the Vietnamese imperial court, Pope Gregory XVI issued papal brief Exponendum Nobis curavit^[40] dividing the Apostolic vicariate of Cochinchina into two vicariates;

• Apostolic vicariate of Eastern Cochinchina, corresponding to Central Vietnam, under Bishop Étienne Cuenot at Gò Thị in Central Vietnam.
• Apostolic vicariate of Western Cochinchina, corresponding to Southern Vietnam, granted to Bishop Dominique Lefebvre.

However, in December 1844, Dominique Lefebvre, who had not yet aware of his new apostolic appointment, was arrested by the Vietnamese in Vĩnh Long and was taken for judiciary trial at Huế, where Lefebvre was sentenced to death but again his death penalty was reprieved by the Vietnamese Emperor Thiệu Trị.

In May 1845, John Percival, an American navy officer on his circumnavigation tour in his frigate USS Constitution, arrived in the Vietnamese port of Danang, proposing for a trade relation.^[48] Dominique Lefebvre, in Vietnamese prison in Huế, wrote a letter and had a Vietnamese Catholic secretly deliver to Percival, pleading Pervical to rescue him.^[48] After reading Lefebvre's letter, Percival led eighty American marines to capture three Vietnamese officials as hostages,^[48] calling for the release of French Bishop Lefebvre. Vietnamese imperial court, however, tricked Percival by saying that the Vietnamese would release Lefebvre when Percival released the Vietnamese hostages. Percival then released the Vietnamese hostages but the Vietnamese did not release Lefebvre.^[48] As he failed to retrieve the French bishop, John Percival informed^[48] Rear Admiral Cécille the commander of French China Seas station at Macau about the captivity of Bishop Lefebvre in Vietnam.

Upon learning of Bishop Lefebvre's incarceration in Vietnam, Rear Admiral Cécille at Macau commissioned capitaine de frégate Fournier-Duplan to led the French frigate Alcmène^[28] from Singapore to Danang in June 1845, where Fournier-Duplan (Đô Rắp Lăng)^[43] delivered Cécille's letter asking the Vietnamese imperial court to release Lefebvre. The tone of the letter was rather reconciliatory,^[48] not aggressive. Ngụy Khắc Tuần again told the Emperor Thiệu Trị that the French had come to politely ask and plead for the release of Lefebvre.^[43] Thiệu Trị then consented to the release of Bishop Dominique Lefebvre, who was taken by Fournier-Duplan on Alcmène to Singapore. Upon release, the Vietnamese told Lefebvre that "The emperor considers that you, a foreigner, had not full knowledge of the laws prohibiting the Christian religion. Therefore, the emperor pardons you and sends you back to your king.".^[48]

Cambodia was then under Siamese domination led by the Siamese commander Chaophraya Bodindecha. In July 1845,^[5]: 99 Nguyễn Tri Phương the governor of An Giang and Hà Tiên provinces in Southern Vietnam led the Vietnamese riparian fleet to attack Southeastern Cambodia in effort to reclaim Vietnamese control over Cambodia, proceeding to capture Phnom Penh in September 1845.^[5]: 100 The combined Cambodian–Siamese forces, unable to resist Vietnamese invasion, retreated to Oudong, where the Siamese commander Bodindecha and Ang Duong the pro-Siamese Cambodian potentate led the defenses against the Vietnamese. Nguyễn Tri Phương led the Vietnamese fleet to attack Oudong in September but the Siamese and Cambodians were able to repel the assault. The Siamese–Vietnamese War of 1845 protracted around the vicinity of Oudong, with each side unable to prevail over the other. Eventually, in December 1845, both the Siamese and the Vietnamese in Cambodia agreed to peace,^[5]: 102 in which Vietnam would accept Ang Duong as King of Cambodia and Ang Duong would send tributes to both Siam and Vietnam.^[5]

Capitaine de frégate Fournier-Duplan delivered Bishop Dominique Lefebvre to Singapore in April 1846. At Singapore, however, Dominique Lefebvre was informed about his apostolic appointment to the newly-created Vicariate of Western Cochinchina so Lefebvre was poised to return to Vietnam. After just one month in Singapore, Dominique Lefebvre departed from Singapore in May along with Father Pierre Duclos,^[47] one of the five priests rescued in 1843 three years earlier, for Southern Vietnam, his vicariate jurisdiction. Both Lefebvre and Duclos attempted to reach Lái Thiêu to join Father Miche there but were arrested by the Vietnamese on their journey. Lefebvre and Duclos were taken to Huế, Lefebvre's second time just one year after being rescued, where both were subjected to judiciary tortures. Father Duclos died during the interrogations. However, the Vietnamese court, contemplating French intervention, decided to send Dominique Lefebvre off on a British merchant ship to Singapore in March 1847.

Apart from Vietnam, Rear Admiral Cécille the commander of the French navy at Macau also brought French complaints on treatment of missionaries to other Asian polities including Joseon Korea. Korea had earlier executed three French MEP priests in 1839. Korea and Vietnam, both anti-Western Confucian states, had been systemically persecuting Christians and the missionaries with vigor. Cécille visited the Ryukyu Kingdom in June 1846,^[49] where Théodore Forcade the Apostolic Vicar of Japan had been residing, to establish a trade relation but did not succeed.^[49] Cécille also visited Nagasaki in July, where he was received with unwelcomeness by the Japanese authorities.^[49] Cécille ended up at Oeyeondo Island of Korea near Boryeong in August 1846, where he attempted to deliver a letter demanding explanation of Korea's execution of French missionaries seven years ago. Korean officials refused to receive the letter, leaving the letter on the rocks.

In early 1847, King Ang Duong of Cambodia sent Cambodian envoys to bring tributary submission to Emperor Thiệu Trị,^[5]: 108 professing to be a vassal of Vietnam. The Cambodian envoys reached Huế in March 1847, having an audience with the Vietnamese Emperor, who accepted Ang Duong as King of Cambodia under Vietnamese vassalage.^[5] Rear Admiral Cécille at Macau, upon knowing of Bishop Dominique Lefebvre's second incarceration at Huế, commissioned his subordinates capitaine de vaisseau Augustin de Lapierre to command the French frigate Gloire and capitaine de frégate Charles Rigault de Genouilly to command Victorieuse to bring those two French warships to Danang. Cécille then resigned from his position as the commander of French navy in China Seas, leaving Lapierre to succeed him and returned to France. Lapierre the new commander of French China Seas Station, along with his subordinate Rigault de Genouilly, left Macau in March 1847 with the two French frigates Gloire and Victorieuse, arriving in Danang, also called Tourane, in April.

This French expedition to Danang in 1847 was different from the two previous occasions (in 1843 and 1845) that this time the French did not only call for the release of missionaries. At Danang, Lapierre (Lạp Biệt Nhĩ)^[43] also urged the Vietnamese court to grant freedom and safety and to cease persecutions of the Christians.^[28]: 73 Emperor Thiệu Trị sent Lý Văn Phức^[43] from the Ministry of Rites to negotiate with Lapierre. The meeting took place at Danang government house. Lapierre gave his letter, written with Chinese characters, to Lý Văn Phức, who refused to take the letter. Enraged, Lapierre shouted at Lý Văn Phức, leaving his letter on the chair and leave.^[43] Lý Văn Phức did not dare to receive the letter from Lapierre and also did not dare to destroy the letter, not knowing what to do, so he returned to Huế. Thiệu Trị saw that Lý Văn Phức cowered before the French, disgracing Vietnam, so Thiệu Trị ordered Lý Văn Phức punished and imprisoned.^[43]

As tension escalated, Emperor Thiệu Trị sent Mai Công Ngôn^[43] as the commander and Đào Trí^[43] as second-in-command to bring Huế forces to defend Danang. Thiệu Trị also sent five Vietnamese copper-plated warships to guard Danang. Both sides claimed that the other side initiated the attack. According to the Vietnamese Đại Nam thực lục, the French began the attack as Lapierre led an amphibious assault on Danang,^[43] where Mai Công Ngôn resisted the French attack and the Vietnamese warships fired on the French frigates. French sources, however, stated that Vietnam began the attack as the Vietnamese warships fired on the French warships Gloire and Victorieuse, who retaliated by bombarding the Vietnamese port of Danang on 15 April 1847.^[28]: 74 Due to technological superiority of the French navy, the Vietnamese in Danang suffered damages and casualties. Forty Vietnamese soldiers died and other ninety were injured.^[43] A mid-ranking Vietnamese officer was also killed in battle. All of the five Vietnamese copper-plated warships were destroyed and sunk. The French also neutralized ten Vietnamese cannons at Danang.^[43]

After the bombardment of Danang, Lapierre did not push for further negotations as the goal of this expedition seemed to be retaliatory.^[28]: 75 Lapierre did not even take Bishop Lefebvre, who had earlier been sent off by Vietnam to Singpapore. Lapierre and his subordinate Rigault de Genouilly left Danang with both frigates Gloire and Victorieuse to return to Macau. The Vietnamese Emperor Thiệu Trị was shocked at the French destructive attack on Danang, becoming depressed and ill. Thiệu Trị punished virtually every Vietnamese commanders and officers of the battle. Any Vietnamese soldiers who were caught by the French and released back were executed.^[43] Both Mai Công Ngôn and Đào Trí were demoted in ranks. Families of the fallen Vietnamese soldiers performed sacrificial rituals for the spirits of the dead on the beach of Danang.^[43] Thiệu Trị expressed his contempt and frustration on the Westerners to his Chief Minister Trương Đăng Quế;

Westerners are inherently cunning. If we lift the ban [on Christianity], the British will hear about it and will also beg to lift the ban on opium. The Westerners are like wolves; we cannot satisfy them! How can we comply to everything according to their wishes? Moreover, Christianity is a heterodoxy. Its harmful effect will lead to wars and external conflicts. Opium is the drug that cause ruin and endanger people's lives. Both of these things [Opium and Christianity] are to be strictly forbidden in the country. I will issue edict, which will be recorded in the national history for future generations, to strictly prohibit them and to prevent any external threats.

^[43]

French bombardment of Danang in April 1847 was the first military conflict between France and Vietnam that would eventually lead to French colonization of Vietnam. In May 1847, Thiệu Trị's delegate in Cambodia performed enthronement ceremony for Ang Duong as Cao Miên quốc vương (高棉國王) or King of Cambodia as a vassal of Vietnam.^[5]: 118 As the agreement had been reached, Nguyễn Tri Phương the Vietnamese commander withdrew Vietnamese forces from Cambodia, ending the Siamese–Vietnamese War.

Just after the bombardment of Danang, in July 1847,^[50] Augustin de Lapierre the commander of French navy in the China Seas brought the same two French frigates Gloire and Victorieuse, along with six hundred French marines,^[50] to Korea during the reign of King Heonjong to demand the Korean reply of the letter Cécille had delivered to Korea a year earlier, perhaps intending to impose a gunboat diplomacy on Korea in the same manner that he had just done to Vietnam. However, due to the rocky nature of the Korean shoreline, both Gloire and Victorieuse hit the reef in a shallow water,^[50] ran aground and wrecked at Gogunsando Island on the coast of Gunsan^[50] in modern North Jeolla Province. Losing both Gloire and Victorieuse, Lapierre and the French marines were stranded on the Gogunsando Island for two months, with the Koreans on the shore giving them food,^[50] until they were rescued by three British frigates in September 1847.

Bishop Dominique Lefebvre, the Apostolic Vicar of Western Cochinchina, at Singapore, was offered by William John Butterworth the Governor of the Straits Settlements to board on a British ship to return to Vietnam. Bishop Lefebvre, out of French patriotism,^[47] refused the British help offer and sought his own way back to Vietnam. Lefebvre managed to sneak into Vietnam in July 1847,^[47] only three months after the bombardment of Danang. Bishop Lefebvre joined Father Miche at Lái Thiêu near Saigon, where Lefebvre would stay for a long time up to the French conquest of Cochinchina until his departure in 1864.^[47]

Seeing the French assault on Danang, the British tried to approach Vietnam. John Francis Davis the Governor of British Hong Kong visited Danang in October 1847,^[28]: 75 proposing a trade relation and presenting a diplomatic letter. Still traumatized after the last French visit, Mai Công Ngôn, who had been stationing in Danang, quickly notified Emperor Thiệu Trị, who sent Tôn Thất Thường, the former Vietnamese envoy to Paris in 1840, to negotiate with the British.^[43] Davis asked to personally present his letter to the Vietnamese Emperor at Huế, to which Tôn Thất Thường refused. After the unsuccessful ten-day negotiation,^[43] Davis was obliged to leave Danang empty-handed. Davis blamed the earlier French bombardment of Danang for his failure to obtain a relation with Vietnam.^[28]: 76 The Vietnamese Emperor Thiệu Trị died in November 1847, shortly after the departure of Davis.^[28] His son succeeded to the Vietnamese throne as the new emperor Tự Đức.

Charles de Montigny returned with the Lagrené Mission to France in 1846, where Montigny composed a report Manual for the French merchant in China (French: Manuel du négociant français en Chine),^[44] narrating what he had learned from joining the Lagrené Mission to China and what could be French commercial benefit potential in China and Vietnam.^[44] This report caught the attention of the French Foreign Minister François Guizot, who was impressed by Montigny's report.^[44] On 20 January 1847, Guizot appointed Montigny as the first-ever French Vice-Consul to Shanghai. By that time, France only had one diplomatic setting in Canton-Macau and Montigny's appointment to Shanghai was a new expansion, which Montigny had to start from scratch. Montigny and his family reached Macau in late 1847, where he did not bother to pay a visit to his superior Forth-Rouen the French Consul at Canton and proceeded directly to Shanghai,^[28]: 81 reaching Shanghai in February 1848.

However, the February Revolution happened in February 1848, when Parisian civilians, who were dissatisfied with the French government of the July Monarchy under King Louis-Phillippe and his Prime Minister François Guizot, who had also been the Foreign Minister, gathered at Boulevard des Capucines,^[51] where French military forces fired on them, resulting in injuries and casualties. The enraged French mob then burnt down Chateaux d'Eau and stormed Tuileries Palace,^[51] where the French king had been residing, prompting King Louis-Phillippe, the Orléans royal family and the Prime Minister Guizot to flee to Britain, ending the July Monarchy regime. The remaining government then proclaimed French Second Republic under the Provisional Government.

Montigny and his family arrived in Shanghai in February 1848 with the French frigate Alcmène, which had earlier gone to Danang in 1845. In accordance with the Whampoa Treaty of 1844, China permitted the French to settle in the five ports including Shanghai. The British, however, arrived earlier and had established the British concession in Shanghai on the western bank of Huangpu River, north of Yangjingbang Canal, in 1845. George Balfour the British Consul at Shanghai invited Montigny for a tour in the British concession. Montigny saw that the British were well-established in Shanghai and the local Chinese officials treated the British with deference.^[44] With French patriotic sentiment, Montigny also wished that the French would be in similar position of honor as the British in Shanghai.^[44] However, Montigny saw that the French should not rely on the British and Montigny should build the French settlement in Shanghai with his own hands.^[44] Balfour invited Montigny to found the French concession within the British concession but Montigny refused.^[28]: 81 Montigny established himself in an old Chinese shack on the southern bank of the Yangjingbang Canal, where Montigny proudly hoisted the French flag.^[28] The Americans also established the American concession in Shanghai in 1848 at Hongkou on the northern bank of Huangpu River.

In March 1848, Chaophraya Bodindecha the Siamese commander in Cambodia enthroned Ang Duong as the King Harireak Reamea of Cambodia under Siamese auspices.^[5]: 123 Father Jean-Claude Miche, who had been with Bishop Lefebvre in Lái Thiêu, was invited by Ang Duong to Cambodia in 1848. Upon his arrival in Cambodia, Father Miche was asked by the Cambodian king Ang Duong to write a letter to the French government to allow French merchants to come to trade in Cambodia.^[52] Ang Duong also expressed his wishes to send Khmer people for education in France. Queen Mother Vara Neak Neang Ros, mother of Ang Duong, expressed her opinion that French presence would deter Vietnamese intervention in Cambodia.^[52] Bodindecha the Siamese governor was delighted upon knowing that the French had bombarded Danang and even proposed to march his Laotian troops to help France attack Vietnam.^[52] Father Miche turned down all these proposals, saying that he was a simple missionary and was not accorded with any political powers.^[52] Chaophraya Bodindecha led the Siamese armies to leave Cambodia in April 1848. Cambodia then became free from both Siamese and Vietnamese military presence. Father Miche took his residence in the Catholic community at Ponhea Lueu.

Montigny initiated his project to establish the French concession in Shanghai without consulting his superior Forth-Rouen at Macau.^[28]: 81 French merchants, however, did not come to trade in Shanghai much due to the economic downturn after the February Revolution.^[28] Without the presence of French merchants, Montigny could not justify his establishment of the concession. When one single French merchant named Remi came to reside with him, Montigny proposed to Lin Gui the Daotai (道臺) or the Chinese governor of Shanghai to grant the land south of Yangjingbang canal for Montigny to establish the French concession.^[28]: 81 Lin Gui, however, rejected this proposal by telling Montigny to consult George Balfour the British Consul in Shanghai, whom Lin Gui considered to exercise jurisdiction over foreign concessions in Shanghai.^[28]: 81 This enraged Montigny, who threatened that Lin Gui's refusal to grant concession to France violated the Article 22 of the Whampoa Treaty and Montigny would bring this matter to the imperial court of Beijing.^[28]: 82 Lin Gui eventually cowered, granting the land for French concession in March 1849.^[28]

In December 1848, Louis-Napoléon Bonaparte, nephew of Emperor Napoleon, was elected as the President of France. France faced fiscal problems during this new republican regime. French government even proposed to suppress the whole French legation in Asia in order to cut the cost^[28]: 93 but the French diplomats in Asia vehemently opposed this idea, saying that the French hard-earned gains in Asia for the last four years would be lost.^[28]: 93 Montigny proposed to this new French government that France should ask China to allow Catholic missionaries in China to go to preach outside of the designated area, to which the French government, who apparently had other concerns, refused, saying that the French missionaries in China had already been accorded with privileges.^[28]: 93

In June 1849, the cholera outbreak reached Bangkok, killing ten thousands of the inhabitants, including Chaophraya Bodindecha the former Siamese general in Cambodia. In his efforts to make Buddhist merits to placate the epidemic, King Rama III of Siam ordered the general merit-making by using his money to buy domesticated animals that were going to be killed for food to release them, saving the animals' lives. The king also encouraged the Siamese populace to do the same by releasing the domesticated animals. The French missionaries, however, saw this practice of releasing animals to make Buddhist merits as superstition^[53] and discouraged the Catholics from following the king's order. Dissatisfied, the king ordered the expulsion of all French missonaries from Siam and all Catholic churches be destroyed.

Among the nine French priests in Bangkok, only Bishop Pallegoix the Apostolic Vicar of Eastern Siam compromised with the king by assigning Phra Wisetsongkhram Pascoal Ribeiro de Albergaria,^[35] a Siamese Catholic offcial of Cambodian–Portuguese Mestizo descent, younger brother of the previous Phra Wisetsongkhram Bento Ribeiro,^[35] to collect domesticated animals from the Catholic churches for the king to release. The king thus became satisfied and rescinded his order to destroy the churches. However, the eight other French missionaries chose to leave Siam rather than to comply with the king's order. These French priests were Pierre Clémenceau, Jean-Baptiste Grandjean, Jean Claudet, Aimé Dupond, Séverin Daniel, Louis Larnaudie, Nicolas Lequeux and Pierre Gibarta, who left Siam for Singapore, Penang and Hong Kong.^[53]

In August 1850, Pope Pius IX issued papal brief Quoties benedicente^[47] creating the Apostolic vicariate of Cambodia, separating from the Western Cochinchina vicariate, with Jean-Claude Miche the Bishop of Dansara at Ponhea Lueu appointed as the first Apostolic Vicar of Cambodia.