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. br br military reserve force is a military organization composed of citizens of a country who combine a military role or career with a civilian career. They are not normally kept under arms and their main role is to be available to fight when a nation mobilizes for total war or to defend against invasion. Reserve forces are generally not considered part of a permanent standing body of armed forces. The existence of reserve forces allows a nation to reduce its peacetime military expenditures while maintaining a force prepared for war. It is analogous to the historical model of military recruitment before the era of standing armies.