During the Japanese occupation of the islands in World War II, there was an extensive Philippine resistance movement, which opposed the Japanese and their collaborators with active underground and guerrilla activity that increased over the years. Fighting the guerrillas – apart from the Japanese regular forces – were a Japanese-formed Bureau of Constabulary, the Kenpeitai, and the Makapili. Postwar studies estimate that around 260,000 people were organized under guerrilla groups and that members of anti-Japanese underground organizations were more numerous. Such was their effectiveness that by the end of World War II, Japan controlled only twelve of the forty-eight provinces.

United States Army Forces in the Far East (USAFFE) was a military formation of the United States Army active from 1941 to 1946. The new command's headquarters was created on 26 July 1941, at No. 1, Calle Victoria, Manila, Luzon, the Philippines, with General Douglas MacArthur as commander. The Chief of Staff was Brigadier General Richard K. Sutherland and the Deputy Chief of Staff was Lieutenant Colonel Richard J. Marshall. The core of this command was drawn from the Office of the Military Advisor to the Commonwealth Government of the Philippines.