What key document established NORTHCOM the new combatant command assigned to defend the US?

The key document that established U.S. Northern Command (NORTHCOM) is the Department of Defense (DoD) directive issued on April 17, 2002. This directive formally created NORTHCOM as a Unified Combatant Command responsible for homeland defense and civil support operations. Its establishment was a response to the September 11 attacks, emphasizing the need for a dedicated command to protect the U.S. and coordinate military response within the homeland.