The Allied occupation of Japan officially began on August 28, 1945, after Japan accepted the surrender terms.
Occupation forces began arriving before the formal surrender ceremony was held. The process was directed by General Douglas MacArthur as Supreme Commander for the Allied Powers. It transformed Japan’s military, political, and economic systems while leaving the Emperor on the throne as a symbolic figure.
The formal surrender was signed on September 2, but that date did not mark the first start of the occupation. Allied personnel had already begun taking control of key facilities and preparing the administration of defeated Japan. The distinction helps explain why August 28 and September 2 both appear in accounts of the war’s conclusion.
The occupation continued until the Treaty of San Francisco came into force in 1952. During those years, Japan was demilitarized, war-crimes trials were held, land and labor reforms were introduced, and a new constitution established parliamentary government and renounced war as a sovereign right.