read the National Defense Act of 1916.

The National Defense Act of 1916 further expanded the Guard's role and guaranteed the State militias' status as the Army's primary reserve
force. Furthermore, the law mandated use of the term "National Guard" for that force. Moreover, the President was given authority, in case of war or
national emergency, to mobilize the National Guard for the duration of the emergency. The number of yearly drills increased from 24 to 48 and annual
training from five to 15 days. Drill pay was authorized for the first time

also dont forget the National Guard Mobilization Act of 1933.

The National Guard Mobilization Act of 1933 made the National Guard of the United States a component of the Army at all times, which could be
ordered into active federal service by the President whenever Congress declared a national emergency.

also dont forget the Total Force Policy of 1973

Following the experience of fighting an unpopular war in Vietnam, the 1973 Total Force Policy was designed to involve a large portion of the
American public by mobilizing the National Guard from its thousands of locations throughout the United States when needed. The Total Force Policy
required that all active and reserve military organizations of the United States be treated as a single integrated force. A related benefit of this
approach is to permit elected officials to have a better sense of public support or opposition to any major military operation. This policy echoes the
original intentions of the founding fathers for a small standing army complemented by citizen-soldiers.

so in reality its not illegal to deploy the citizen soldiers overseas. we have seen in the past of National Guard troops being deployed overseas long
before the Iraq war came.