Vietnam's independence was gradually eroded by France in a series of military conquests from 1859 until 1885 when the entire country became part of French Indochina. The French administration imposed significant political and cultural changes on Vietnamese society. A Western-style system of modern education was developed, and Christianity was propagated widely in Vietnamese society. Most of the French settlers in Indochina were concentrated in Cochinchina (southern third of Vietnam whose principal city was Saigon).

Developing a plantation economy to promote the exports of tobacco, indigo, tea and coffee, the French largely ignored increasing calls for self-government and civil rights. A nationalist political movement soon emerged, with leaders such as Phan Boi Chau, Phan Chu Trinh, Phan Dinh Phung, Emperor Ham Nghi and Ho Chi Minh calling for independence. However, the French maintained control of their colonies until World War II, when the Japanese war in the Pacific triggered the invasion of French Indochina in 1941.
This event was preceded by the establishment of the Vichy French administration, a puppet state of Nazi Germany then ally of the Japanese Empire. The natural resources of Vietnam were exploited for the purposes of the Japanese Empire's military campaigns into the British Indochinese colonies of Burma, the Malay Peninsula and India.