The Eighth Army is a U.S. field army which commands all United States Army forces in South Korea. It is headquartered at the Camp Humphreys in the Anjeong-ri of Pyeongtaek, South Korea. Eighth Army relocated its headquarters from Yongsan to Camp Humphreys in the summer of 2017. It is the only field army in the U.S. Army. It is responsible to United States Forces Korea and United States Army, Pacific.

Japan was occupied and administered by the Allies of World War II from the surrender of the Empire of Japan on September 2, 1945, at the war's end until the Treaty of San Francisco took effect on April 28, 1952. The occupation, led by the American military with support from the British Commonwealth and under the supervision of the Far Eastern Commission, involved a total of nearly one million Allied soldiers. The occupation was overseen by the US General Douglas MacArthur, who was appointed Supreme Commander for the Allied Powers by the US President Harry S. Truman; MacArthur was succeeded as supreme commander by General Matthew Ridgway in 1951. Unlike in the occupations of Germany and Austria, the Soviet Union had little to no influence in Japan, declining to participate because it did not want to place Soviet troops under MacArthur's direct command. And unlike Germany, the Japanese government still remained in place throughout the occupation.