Originally Posted by jason_els

Yes, though we generally call it the National Guard. These forces are at the disposal of the governors of their respective states and used in times of disaster or extreme civil unrest. They're a holdover from the days when communication and travel was such that the country could be invaded and half conquered before anybody in Philadelphia (or New York or Washington) found out. The president can federalize national guard units at his discretion. National guard units may be deployed for combat duty abroad but they can also be used to enforce federal law. Eisenhower did this in Arkansas when the governor refused to desegregate the schools following a Supreme Court decision and used the state police to bar black students from entering white schools.