French Indochina was formed in the late 19th century by combining three Vietnamese regions (Tonkin, Annam and Cochinchina) with Cambodia, Laos and Guangzhouwan. With the fall of France in 1940, the control of the colony shifted to the Vichy French who allowed military occupation by Imperial Japan.

With a weakened French position in Indochina, Thailand waged the Franco-Thai War in 1940-41 to reclaim previously-lost territories. A peace treaty brokered by Japan granted disputed border lands in Cambodia and Laos to Thailand.

From March-August 1945 Japan assumed complete control of French Indochina. At the conclusion of WWII, the French tried to reassert control over the region but were opposed by the Viet Minh, a coalition of nationalists and Communists led by Nguyen Sinh Cung (later named Ho Chi Minh). The Viet Minh launched a lengthy guerrilla war from 1946-1954 known as the First Indochina War.