I would like to post my reading of the Constitution insofar as I believe the military was set up.
1) The Federal Government has the authority to maintain a Navy
2) The Federal Government has the authority to raise armies, but no funding can last more than two years
3) The commander in chief has the authority to call up the militia (this is different from maintaining the militia)
There are some other applicable clauses, but these are sufficient to make the broad point. As the founders separated legal authority between Federal and State government, they also separated military power as well. Since land was designated to states the states would be in charge of their own land forces. Since the seas were not owned by any one state the seas would be protected by the Federal forces - the Navy (which does not have the 2 year limit on funding). There was never supposed to be a standing army for the Commander in Chief to direct at his hearts content. He first needed to seek approval from Congress and then call up militias from the several states. There was room for a limited authority of the Federal government to train and regulate the militias, but the militias were supposed to be under states.
Why is this a good system? We are separated from every country (except Canada and Mexico) by major oceans. A strong Navy should be sufficient to prevent or repel attack or invasion from foreign nations. Separating the authority meant there were two checks on using Army, one from Congress and one from States. I cannot imagine any situation like Pearl Harbor or 9/11 wherein the states would refuse the call in direct defiance of the Constitution. However, I can clearly imagine that if the President had to consider the wishes of the citizens of Texas and Florida (which contribute disproportionately to the armed forces) there might be less desire to seek action in Syria, or at least tell Rick Scott and Rick Perry what the goal is. Even if Obama got the Navy involved he would know that there would be a limit to his ability to mire us down into a Muslim vs. Muslim vs. Muslim genocide/civil war.
Like it or not that is the system the founders intended, and they intended it specifically to prevent unpopular unnecessary wars that European nations frequently got into because of someone's big mouth or injured ego.
* The other major reason for the given separation of powers is not in play. The founders also believed that the Federal Government should not have a military capable of occupying individual States (since a Navy is not an occupying force).
Apologies - I made a minor edit on point 3 (added the parenthetical statement) and updated before remembering that this would top post the entire thing.