United States Northern Command (USNORTHCOM, or informally just NORTHCOM) is a Unified Combatant Command of the United States Military. Created on October 1, 2002 in the aftermath of the September 11, 2001 attacks, its mission is to protect the United States homeland and support local, state, and federal authorities. The support that USNORTHCOM provides to civil authorities is limited by the Posse Comitatus Act which limits the role of the U.S. military in civil law enforcement.
USNORTHCOM’s Area of Responsibility (AOR) includes air, land and sea approaches and encompasses the continental United States, Alaska, Canada, Mexico and the surrounding water out to approximately 500 nautical miles (930 km). It also includes the Gulf of Mexico and the Straits of Florida. The defense of Hawaii and US territories in the Pacific is the responsibility of U.S. Pacific Command. The defense of Puerto Rico and the U.S. Virgin Islands is the responsibility of U.S. Southern Command. The commander of USNORTHCOM is responsible for theater security cooperation with Canada and Mexico.
USNORTHCOM is composed of several standing Joint Task Forces (JTFs) previously assigned to United States Joint Forces Command (USJFCOM): Joint Force Headquarters National Capital Region, Joint Task Force Alaska, and Joint Task Force North. USNORTHCOM service components include U.S. Fifth Army/ARNORTH, First Air Force/AFNORTH, MARFORNORTH, and Fleet Forces Command.