Douglas MacArthur became Supreme Commander for the Allied Powers during Japan’s postwar occupation.
The position was created on August 14, 1945, as Japan’s surrender approached. MacArthur directed the United States-led Allied occupation from his headquarters in Tokyo. Although the title referred to the Allied Powers, the occupation structure was dominated by the United States, with MacArthur exercising broad authority over Japan’s demilitarization and political reconstruction.
MacArthur also played a direct role in the surrender ceremony. On September 2, 1945, he accepted Japan’s surrender on behalf of the Allied Powers aboard USS Missouri and signed the Japanese Instrument of Surrender in his capacity as Supreme Commander.
His occupation administration issued directives affecting Japan’s government, military, education, and economy. The occupation ended in 1952 when the Treaty of San Francisco came into force, although the title and its associated authority had already shaped Japan’s transition from wartime empire to a postwar state.