The American military system developed from a combination of the professional, national Continental Army, the state militias and volunteer regiments of the American Revolutionary War, and the similar post-Revolutionary War American military units under the Militia Act of 1792. These provided a basis for the United States Army's organization, with only minor changes, until the creation of the modern National Guard in 1903. The Militia Act provided for the use of volunteers who could be used anywhere in time of war, in addition to the State militias who were restricted to local use within their States for short periods of time. Even today's professional United States Army, which is augmented by the Army Reserve and Army National Guard, has a similar system of organization: a permanent, professional core, and additional units which can be mobilized in emergencies or times of war.