In March 1945, Japan launched the Second French Indochina Campaign to oust the Vichy French and formally installed Emperor Bảo Đại as head of the nominally independent Empire of Vietnam. The Japanese arrested and imprisoned most of the French officials and military officers remaining in the country.
Japanese forces allowed the Việt Minh and other nationalist groups to take over public buildings and weapons without resistance, which began the August Revolution. On August 25, Hồ Chí Minh was able to persuade Emperor Bảo Đại to abdicate. Bảo Đại was appointed "supreme advisor" to the new Việt Minh-led government in Hanoi.
Following the August Revolution (1945) organized by the Việt Minh, Hồ Chí Minh became Chairman of the Provisional Government (Premier of the Democratic Republic of Vietnam) and issued a Proclamation of Independence of the Democratic Republic of Vietnam.
On September 13, 1945, a Franco-British task force landed in Java, main island of the Dutch East Indies (for which independence was being sought by Sukarno), and Saigon, capital of Cochinchina (southern part of French Indochina), both being occupied by the Japanese and ruled by Field Marshal Hisaichi Terauchi, Commander-in-Chief of Japan's Southern Expeditionary Army Group based in Saigon.
Allied troops in Saigon were an airborne detachment, two British companies of the Indian 20th Infantry Division and the French 5th Colonial Infantry Regiment, with British General Sir Douglas Gracey as supreme commander. The latter proclaimed martial law on September 21. The following night the Franco-British troops took control of Saigon.
On 23 September 1945, with the knowledge of the British commander in Saigon, French forces overthrew the local DRV (the Democratic Republic of Vietnam) government, and declared French authority restored in Cochinchina.
In Saigon, with violence between rival Vietnamese factions and French forces increasing, the British commander, General Sir Douglas Gracey, declared martial law. On 24 September, the Việt Minh leaders responded with a call for a general strike.
On October 9, 1945, General Leclerc arrived in Saigon, accompanied by French Colonel Massu's March Group (Groupement de marche). Leclerc's primary objectives were to restore public order in south Vietnam and to militarize Tonkin (north Vietnam). Secondary objectives were to wait for French backup in view to take back Chinese-occupied Hanoi, then to negotiate with the Việt Minh officials.