After that the wars were overseas. That was an Army function. In the 20th Century, the National Guard which had Militia roots was turned into part of the Army with members enlisted in the U.S. Army, and more recently in the U.S. Air Force. Thus Militia could not serve overseas in foreign war but the Army could. The Second Amendment is addressed to Congress and to Federal power.
History suggests that groups have been authorized or encouraged to organize as volunteer Militia.
However, operations by armed groups is a matter for government. State power over groups which act or parade as military was affirmed by the Supreme Court. The National Guard was called into federal service, and for more than the 90 day limit that had been in effect from 1792 until this Century. Extended wartime duty left most states with no militia. This in turn led to the creation of State Guards.