What section of the military is the Corps area and the National Guard of the United States?
Corps area:  Each corps area included divisions of the Regular Army, Organized Reserve and National Guard of the United States. National Guard of the United States: The National Guard of the United States, part of the reserve components of the United States Armed Forces, is a reserve military force, composed of National Guard military members or units of each state and the territories of Guam, of the Virgin Islands, and of Puerto Rico, as well as of the District of Columbia, for a total of 54 separate organizations.
reserve