SCAP was the abbreviation for the Supreme Commander for the Allied Powers, the occupation authority led by Douglas MacArthur in postwar Japan.
The title was created in August 1945 as the Allies prepared to occupy Japan. MacArthur held the position and exercised authority over Japan through the occupation headquarters in Tokyo.
SCAP issued directives to the Japanese government covering demilitarization, political reform, education, labor policy, and other areas. Although the occupation was American-led, it was formally conducted in the name of the Allied powers.
The abbreviation can be confusing because “SCAP” referred both to MacArthur’s position and, in common usage, to his headquarters and administrative organization. “GHQ” was another term used for the General Headquarters in Tokyo, but SCAP was the distinctive title of the supreme occupation authority. The occupation formally ended in 1952 after the Treaty of San Francisco entered into force.