State defense forces are distinct from their state's National Guard in that they cannot become federal entities. All state National Guard personnel (to include the National Guard of the District of Columbia, the Commonwealth of Puerto Rico and the territories of Guam and the Virgin Islands) can be federalized under the National Defense Act Amendments of 1933 with the creation of the National Guard of the United States. This provides the basis for integrating units and personnel of the Army National Guard into the U.S. Army and, since 1947, units and personnel of the Air National Guard into the U.S. Air Force.[1]