SCAP was the acronym for the Allied occupation command established in Japan after its 1945 surrender.
SCAP stands for Supreme Commander for the Allied Powers. The title referred both to General Douglas MacArthur, who held the position, and commonly to the occupation headquarters and administration operating under his authority. The occupation began in August 1945 after Japan’s surrender.
SCAP issued directives to the Japanese government and supervised demilitarization, political reform, economic changes, and the development of a new constitutional system. Although the occupation was Allied in name, the United States exercised dominant control over its administration.
In Japan, the occupation headquarters was often called GHQ, meaning General Headquarters. That term is related but not identical to SCAP. The occupation ended when the San Francisco Peace Treaty took effect on 28 April 1952. MacArthur remained SCAP until President Harry S. Truman relieved him in 1951, after which General Matthew Ridgway succeeded him.