Cochinchina Campaign The Cochinchina campaign ( ; ; ; 1858 – 1862 ) , fought between the French and the Spanish on one side and the Vietnamese on the other , began as a limited punitive campaign and ended as a French war of conquest . The war concluded with the establishment of the French colony of Cochinchina , a development that inaugurated nearly a century of French colonial dominance in Vietnam . Background . The French had few pretexts to justify their imperial ambitions in Indochina . In the early years of the 19th century some Frenchmen believed that the Vietnamese emperor Gia Long owed the French a favour for the help French troops had given him in 1802 against his Tây Sơn enemies , but it soon became clear that the Gia Long felt no more bound to France than he did to China , which had also provided help . Gia Long felt that as the French government did not honour their agreement to assist him in the civil war — the Frenchmen who helped him were volunteers and adventurers not government units — he was not obliged to give them favours . Certainly , he and his successor Minh Mạng flirted with the French . Although the Vietnamese soon learned to reproduce the elaborate Vaubanesque fortresses that had been built at the end of the 18th century by French engineers , and no longer needed French technical assistance in the art of fortification , they were still interested in buying French cannon and rifles . But this limited contact with the French counted for little . Neither Gia Long nor Minh Mạng had any intention of coming under French influence . But the French were not prepared to be brushed off quite so easily . As so often during the era of European colonial expansion , religion offered an excuse for intervention . French missionaries had been active in Vietnam since the 17th century , and by the middle of the 19th century there were perhaps 300 , 000 Roman Catholic converts in Annam and Tonkin . Most of their bishops and priests were either French or Spanish . Most Vietnamese disliked and suspected this sizeable Christian community and its foreign leaders . The French , conversely , began to feel responsible for their safety . Harassment of the Christians eventually provided France with a respectable pretext for attacking Vietnam . The tension built up gradually . During the 1840s , persecution or harassment of Catholic missionaries in Vietnam by the Vietnamese emperors Minh Mạng and Thiệu Trị evoked only sporadic and unofficial French reprisals . The decisive step towards the establishment of a French colonial empire in Indochina was not taken until 1858 . In 1857 , the Vietnamese emperor Tự Đức ( r . 1848 – 83 ) executed two Spanish Catholic missionaries . This was neither the first nor the last such incident , and on previous occasions the French government had overlooked such provocations . But this time , Tự Đức ' s timing was inopportune , as it coincided with the Second Opium War . France and Britain had just despatched a joint military expedition to the Far East to chastise China , with the result that the French had troops on hand with which to intervene in Annam . In November 1857 , Napoleon III of France authorised Admiral Charles Rigault de Genouilly to send a punitive expedition to Vietnam . In September 1858 , a joint French and Spanish expedition landed at Tourane ( Da Nang ) and captured the town . Tourane and Saigon . The allies expected an easy victory , but the war did not at first go as planned . The Vietnamese Christians did not rise in support of the French ( as the missionaries had been confidently predicting they would ) , Vietnamese resistance was more stubborn than had been expected , and the French and Spanish found themselves besieged in Tourane by a Vietnamese army under the command of Nguyễn Tri Phương . The Siege of Tourane lasted for nearly three years , and although there was little fighting disease took a heavy toll of the allied expedition . The garrison of Tourane was reinforced from time to time , and occasionally mounted local attacks against the Vietnamese positions , but was unable to break the siege . In October 1858 , shortly after his capture of Tourane , Rigault de Genouilly cast around for somewhere else to strike the Vietnamese . Realising that the French garrison at Tourane was unlikely to achieve anything useful , he weighed up the possibility of action in either Tonkin or Cochinchina . He considered and rejected the possibility of an expedition to Tonkin , which would require a large - scale uprising by the Christians to have any chance of success , and in January 1859 proposed to the navy ministry an expedition against Saigon in Cochinchina , a city of considerable strategic significance as a source of food for the Vietnamese army . The expedition was approved , and in early February , leaving " capitaine de vaisseau " Thoyon at Tourane with a small French garrison and two gunboats , Rigault de Genouilly sailed south for Saigon . On 17 February 1859 , after forcing the river defences and destroying a series of forts and stockades along the Saigon river , the French and Spanish captured Saigon . French marine infantry stormed the enormous Citadel of Saigon , while Filipino troops under Spanish command threw back a Vietnamese counterattack . The allies were not strong enough to hold the citadel , and on 8 March 1859 blew it up and set fire to its rice magazines . In April , Rigault de Genouilly returned to Tourane with the bulk of his forces to reinforce Thoyon ' s hard - pressed garrison , leaving " capitaine de frégate " Bernard Jauréguiberry ( the future French navy minister ) at Saigon with a Franco - Spanish garrison of around 1 , 000 men . The capture of Saigon proved to be as hollow a victory for the French and Spanish as their earlier capture of Tourane . Jauréguiberry ' s small force , which suffered substantial losses in a surprise attack on a Vietnamese fortification to the west of Saigon on 21 April 1859 , was forced to remain behind its defences thereafter . Meanwhile , the French government was distracted from its Far Eastern ambitions by the outbreak of the Austro - Sardinian War , which tied down large numbers of French troops in Italy . In November 1859 , Rigault de Genouilly was replaced by Admiral François Page , who was instructed to obtain a treaty protecting the Catholic faith in Vietnam but not to seek any territorial gains . Page opened negotiations on this basis in early November , but without result . The Vietnamese , aware of France ' s distraction in Italy , refused these moderate terms and spun out the negotiations in the hope that the allies would cut their losses and abandon the campaign altogether . On 18 November 1859 Page bombarded and captured the Kien Chan forts at Tourane , but this allied tactical victory failed to change the stance of the Vietnamese negotiators . The war continued into 1860 . During the second half of 1859 and throughout 1860 , the French were unable to substantially reinforce the garrisons of Tourane and Saigon . Although the Austro - Sardinian War soon ended , by early 1860 the French were again at war with China , and Page had to divert most of his forces to support Admiral Léonard Charner ' s China expedition . In April 1860 , Page left Cochinchina to join Charner at Canton . Meanwhile , in March 1860 , a Vietnamese army around 4 , 000 strong began to besiege Saigon . The defence of Saigon was entrusted to " capitaine de vaisseau " d ' Ariès . The Franco - Spanish force in Saigon , only 1 , 000 men strong , had to support a siege by greatly superior numbers from March 1860 to February 1861 . Realising that they could not hold both Saigon and Tourane , the French evacuated the garrison of Tourane in March 1860 , bringing the Siege of Tourane to an inglorious end . Ky Hoa and Mỹ Tho . Although the French had evacuated Tourane , they successfully held out in Saigon for the remainder of 1860 . But they were not strong enough to break the Vietnamese siege of Saigon . The military stalemate was only broken in early 1861 , as a result of the ending of the war with China . Admirals Charner and Page were now free to return to Cochinchina and resume the campaign around Saigon . A naval armada of 70 ships under Charner ' s command and 3 , 500 soldiers under the command of General de Vassoigne were transferred from northern China to Saigon . Charner ' s squadron , the most powerful French naval force seen in Vietnamese waters before the creation of the French Far East Squadron on the eve of the Sino - French War ( August 1884 – April 1885 ) , included the steam frigates " Impératrice Eugénie " and " Renommée " ( Charner and Page ' s respective flagships ) , the corvettes " Primauguet " , " Laplace " and " Du Chayla " , eleven screw - driven despatch vessels , five first - class gunboats , seventeen transports and a hospital ship . The squadron was accompanied by half a dozen armed lorchas purchased in Macao . With this powerful reinforcement , the allies eventually began to gain the upper hand . On 24 and 25 February 1861 , the French and Spanish in Saigon successfully assaulted the Vietnamese siege lines , defeating marshal Nguyễn Tri Phương ' s besieging Vietnamese army in the battle of Ky Hoa . The Vietnamese fought bitterly to defend their positions , and allied casualties were considerable . The victory at Ky Hoa allowed the French and Spanish to move to the offensive . In April 1861 , Mỹ Tho fell to the French . An assault force under the command of " capitaine de vaisseau " Le Couriault du Quilio , supported by a small flotilla of gunboats , advanced on Mỹ Tho from the north along the Bao Dinh Ha creek , and between 1 and 11 April destroyed several Vietnamese forts and fought its way along the creek to the environs of Mỹ Tho . Le Couriault de Quilio gave orders for an assault on the town on 12 April , but in the event the assault was not necessary . A flotilla of warships under the command of Admiral Page , who had been sent by Charner to sail up the Mekong River to attack Mỹ Tho by sea , appeared off the town on the same day . Mỹ Tho was occupied by the French on 12 April 1861 without a shot being fired . In March 1861 , shortly before the capture of Mỹ Tho , the French again offered terms to Tự Đức . This time the terms were considerably harsher than those offered by Page in November 1859 . The French demanded the free exercise of Christianity in Vietnam , the cession of Saigon province , an indemnity of 4 million piastres , freedom of commerce and movement inside Vietnam and the establishment of French consulates . Tự Đức was only prepared to concede on the free exercise of religion , and rejected the other French terms . The war went on , and after the fall of Mỹ Tho the French raised their territorial claims to include Mỹ Tho province as well as Saigon province . Unable to confront the French and Spanish forces in battle , Tự Đức resorted to guerilla warfare , sending his agents into the conquered Vietnamese provinces to organise resistance to the invaders . Charner responded on 19 May by declaring Saigon and Mỹ Tho provinces to be in a state of siege . French columns roved through the Cochinchinese countryside , fanning popular resistance by the brutality with which they treated suspected insurgents . Charner had ordered them not to offer violence to peaceful villagers , but these orders were not always obeyed . The Vietnamese guerillas on occasion posed a serious threat to the French . On 22 June 1861 the French post at Gò Công was attacked , unsuccessfully , by 600 Vietnamese insurgents . Bien Hoa and Vĩnh Long . The Capture of Mỹ Tho was Charner ' s last military success . He returned to France in the summer of 1861 , and was replaced in command of the Cochinchina expedition by Admiral Louis - Adolphe Bonard ( 1805 – 67 ) , who arrived in Saigon at the end of November 1861 . A mere fortnight after his arrival in Saigon , in reprisal for the loss of the French lorcha " Espérance " and all her crew in an ambush , Bonard mounted a major campaign to overrun Đồng Nai Province . Biên Hòa , the provincial capital , was captured by the French on 16 December 1861 . The French followed up their victory at Biên Hòa by capturing Vĩnh Long on 22 March 1862 , in a brief campaign mounted by Admiral Bonard in reprisal for Vietnamese guerilla attacks on French troops around Mỹ Tho . In the most serious of these incidents , on 10 March 1862 , a French gunboat leaving Mỹ Tho with a company of infantry aboard suddenly exploded . Casualties were heavy ( 52 men killed or wounded ) , and the French were convinced that the gunboat had been sabotaged by insurgents directed by the governors of Vĩnh Long Province . Ten days later , Bonard anchored off Vĩnh Long with a flotilla of eleven despatch vessels and gunboats and a Franco - Spanish landing force of 1 , 000 troops . In the afternoon and evening of 22 March , the French and Spanish assaulted the Vietnamese batteries entrenched before Vĩnh Long and captured them . On 23 March they entered the citadel of Vĩnh Long . Its defenders retreated to a fortified earthwork at My Cui , 20 kilometres to the west of Mỹ Tho , but two allied columns pursued them and drove them from My Cui while a third cut off their retreat northwards . Vietnamese casualties at Vĩnh Long and My Cui were heavy . The fall of Vĩnh Long , coming after the loss of Mỹ Tho and Bien Hoa , disheartened the Court of Huế , and in April 1862 Tự Đức let it be known that he was willing to make peace . In May 1862 , following preliminary discussions at Huế , the French corvette " Forbin " sailed to Tourane to receive Vietnamese plenipotentiaries charged with concluding peace . The Vietnamese were given three days to produce their ambassadors . The sequel was described by Colonel Thomazi , the historian of the French conquest of Indochina : On the third day , an old paddlewheel corvette , the " Aigle des Mers " , was seen slowly leaving the Tourane river . Her beflagged keel was in a state of dilapidation that excited the laughter of our sailors . It was obvious that she had not gone to sea for many years . Her cannons were rusty , her crew in rags , and she was towed by forty oared junks and escorted by a crowd of light barges . She carried the plenipotentiaries of Tự Đức . " Forbin " took her under tow and brought her to Saigon , where the negotiations were briskly concluded . On 5 June a treaty was signed aboard the vessel " Duperré " , moored before Saigon . The peace . By then the French were not in a merciful mood . What had begun as a minor punitive expedition had turned into a long , bitter and costly war . It was unthinkable that France should emerge from this struggle empty - handed . Tự Đức ' s minister Phan Thanh Giản signed a treaty with Admiral Bonard and the Spanish representative Colonel Palanca y Gutierrez on 5 June 1862 . The Treaty of Saigon required Vietnam to permit the Catholic faith to be preached and practised freely within its territory ; to cede the provinces of Biên Hòa , Gia Định and Định Tường and the island of Poulo Condore to France ; to allow the French to trade and travel freely along the Mekong River ; to open Tourane , Quảng Yên and Ba Lac ( at the mouth of the Red River ) as trading ports ; and to pay an indemnity of a million dollars to France and Spain over a ten - year period . The French placed the three southern Vietnamese provinces under the control of the navy ministry . Thus , casually , was born the French colony of Cochinchina , with its capital at Saigon . Aftermath . In 1864 the three southern provinces ceded to France were formally constituted as the French colony of Cochinchina . Within three years , France ' s new colony doubled in size . In 1867 Admiral Pierre de la Grandière forced the Vietnamese to cede the provinces of Châu Đốc , Hà Tiên and Vĩnh Long to France . The Vietnamese emperor Tự Đức initially refused to accept the validity of this cession , but eventually recognized French dominion over the six provinces of Cochinchina in the 1874 Treaty of Saigon , negotiated by Paul - Louis - Félix Philastre after the military intervention of Francis Garnier in Tonkin . The Spanish , who had played a junior role in the Cochinchina campaign , received a share of the indemnity but made no territorial acquisitions in Vietnam . Instead , they were encouraged by the French to seek a sphere of influence in Tonkin . Nothing came of this suggestion , however , and Tonkin ultimately fell under French control also , becoming a French protectorate in 1883 . Perhaps the most important factor in Tự Đức ' s decision to make peace was the threat posed to his authority by a serious uprising in Tonkin led by the Catholic nobleman Le Bao Phung , who claimed descent from the old Lê Dynasty . Although the French and Spanish rejected Le ' s offer of an alliance against Tự Đức , the insurgents in Tonkin were able to inflict several defeats on Vietnamese government forces . The end of the war with France and Spain allowed Tự Đức to overwhelm the insurgents in Tonkin and restore government control there . Le Bao Phung was eventually captured , tortured and put to death .