A corps area was a geographically-based organizational structure of the United States Army used to accomplish administrative, training, and tactical tasks from 1920 to 1942. Each corps area included divisions of the Regular Army, Organized Reserve, and National Guard of the United States. Developed as a result of serious mobilization problems during World War I, this organization provided a framework to rapidly expand the Army in times of war or national emergency, such as the Great Depression.

The Philippine Department was a regular United States Army organization whose mission was to defend the Philippine Islands and train the Philippine Army. On 9 April 1942, during World War II, the organization surrendered to the Japanese. The department and its sub-units were predominantly under the command of American officers, including an American general, while the majority of the troops were enlisted Filipinos, known as the Philippine Scouts (PS). The primary force of this department was the Philippine Division. Of the 22,532 troops, 10,473 were members of the Philippine Division itself.