Vietnam's independence has been gradually eroded by France—aided by large Catholic collaborator militias—in a series of military conquests between 1859 and 1885, after which the entire country becomes part of French Indochina, formed in October 1887 from Annam, Tonkin, Cochinchina (which together form modern Vietnam) and the Kingdom of Cambodia.

The French administration imposes significant political and cultural changes on Vietnamese society.

A Western-style system of modern education is developed, and Roman Catholicism is propagated widely in Vietnamese society.

Most of the French settlers in Indochina are concentrated in Cochinchina—the southern third of Vietnam—based around the city of Saigon.