High Quality Content by WIKIPEDIA articles! A Corps area was a geographically-based organizational structure (area command) of the United States Army used to accomplish domestic 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 organizational scheme provided a framework to rapidly expand the Army in time of war or national emergency such as the Great Depression.