We used to adhere to the Constitution prior to World War II. The Army reverted to 'reserve' status (i.e. militia) during peacetime. After World War II (1948, I believe) the old War Department was abolished and replaced with the Department of Defense. We then maintained a standing army at all times, using the pretense of a 'cold war' to justify it, somewhat, constitutionally. It was at that time that the Army Air Corps became the USAF, I believe (I don't feel like Googling right now to be sure).
Personally, I think it was the idea of placing command of the nuclear arsenal in the hands of fifty governors that prompted the change, but I wasn't around then so I could be mistaken.
When the Berlin wall fell, and the Cold War was declared at an end, President Bush, and President Clinton after him, began scaling back the Army, shifting much of the personnel to militia status. We still maintain a standing army, although significantly smaller than during its' cold war heyday. Now, when I hear people complaining that the war is 'putting a strain on the National Guard', I just tell them to blame the Constitution. Although, to be fair, the merger of the National Guard and the Army Reserve does present some difficulties. The Constitution authorizes the Congress to disipline that part of the militia in service to the United States government, but does not state how that service comes to be (unless it refers to wartime service, but that is mentioned in a seperate paragraph). In my humble opinion, the organized militia is divided between the Federal Militia and the National Guard, which are under the command of the governors. The merger of the guard and reserve blurrs that distinction, however.
The unorganized militia is composed of the rest of us.
Interestingly, in the court decision on Miller, it was noted that the law at that time required members of the militia to report for duty bearing their own arms, of the type in general use at the time. I would gather that was the wording of the US Code at that time, although I'm sure it has been changed since.
Quod scripsi, scripsi.