The United States Northern Command (USNORTHCOM) is one of the eleven unified combatant commands of the United States Department of Defense. The command is tasked with providing military support for non-military authorities in the U.S., and protecting the territory and national interests of the United States within the continental United States, Puerto Rico, Canada, Mexico, the Bahamas, Greenland (Denmark) and the air, land and sea approaches to these areas. It is the U.S. military command which, if applicable, would be the primary defender against an invasion of the U.S.