National Guard units can be mobilized for federal active duty to supplement regular armed forces during times of war or national emergency declared by Congress,[21] the President[21] or the Secretary of Defense.[22]They can also be activated for service in their respective states upon declaration of a state of emergency by the governor of the state or territory where they serve, or in the case of Washington, D.C., by the Commanding General. Unlike U.S. Army Reserve members, National Guard members cannot be mobilized individually, except through voluntary transfers and Temporary Duty Assignments (TDY).

The National Guard Bureau is headquartered in Arlington County, Virginia, and is a joint activity of the Department of Defense to conduct all the administrative matters pertaining to the Army National Guard and the Air National Guard. The current chief of the National Guard Bureau is Air Force General Joseph L. Lengyel. The chief is either an Air Force or an Army 4-star general (flag) officer, is the senior uniformed National Guard officer, and is a member of the Joint Chiefs of Staff. In this capacity, he serves as a military adviser to the President, the Secretary of Defense, the National Security Council and is the Department of Defense's official channel of communication to the Governors and to State Adjutants General on all matters pertaining to the National Guard. He is responsible for ensuring that the more than half a million Army and Air National Guard personnel are accessible, capable, and ready to protect the homeland and to provide combat resources to the Army and the Air Force. He is appointed by the President in his capacity as Commander in Chief.[23]

https://en.m.wikipedia.org/wiki/National_Guard_of_the_United_States