A joint French and Spanish expedition attacked the Vietnamese port of Tourane (Đà Nẵng), aiming to pressure the Nguyễn court and gain a military foothold. The landing opened what became the Cochinchina Campaign, shifting the conflict from diplomatic disputes over missionaries into open warfare.
Vietnamese forces contained the expedition at Tourane, preventing the attackers from advancing inland. Disease and supply problems weakened the expedition, showing that holding a northern base would be costly and uncertain.
After failing to break out from Tourane, Admiral Rigault de Genouilly decided to strike south at Saigon, a strategic area linked to food supplies and river routes. This choice shifted the war’s center of gravity from central Vietnam to the Mekong region.
The expedition seized Saigon, giving France a strong position in southern Vietnam. Vietnamese forces then tried to isolate the invaders, beginning a prolonged siege that tied down both sides and made control of nearby provinces the next objective.
After nearly 19 months under pressure, the French and Spanish withdrew from Tourane. The evacuation confirmed that the conquest would be pursued through southern bases like Saigon rather than from central Vietnam.
French and Spanish troops attacked and captured the Vietnamese fortified lines at Kỳ Hòa near Saigon. The victory weakened Vietnamese efforts to retake the city and opened the way for France to expand into surrounding provinces.
The allied force captured Mỹ Tho in the Mekong Delta, extending French control beyond Saigon into key river and agricultural areas. Each new occupation increased pressure on the Nguyễn court by shrinking its authority in the south.
Admiral Louis-Adolphe Bonard was placed in command of French forces in Cochinchina, formalizing a more direct occupation and administration. Under his command, French operations focused on securing provinces around Saigon to turn battlefield gains into lasting control.
Vietnam signed the Treaty of Saigon, transferring Saigon and three southern provinces (Biên Hòa, Gia Định, Định Tường) to France, along with other concessions such as indemnities and openings for trade and missions. The agreement gave France its first formal territorial base in Vietnam, laying the foundation for the colony of Cochinchina.
A follow-up treaty at Huế confirmed key parts of the earlier Saigon agreement and reinforced France’s growing leverage over Vietnam’s external relations. This helped turn a wartime occupation into a recognized colonial arrangement, even as resistance continued.
Governor Pierre-Paul de La Grandière organized the occupation of the remaining western provinces, including Vĩnh Long, Châu Đốc (An Giang area), and Hà Tiên. With this move, French control effectively extended across southern Vietnam and the Mekong Delta, completing the annexation of Cochinchina in practice.
Vietnamese official Phan Thanh Giản, associated with the 1862 negotiations and later governance in the western provinces, died by suicide after France completed its takeover of southern Vietnam. His death became a symbol of the Nguyễn court’s weakening position and the irreversible shift to direct French rule in Cochinchina.
French conquest and annexation of Cochinchina (1858–1867)