| In the United States, this concept is embodied in the fact that the President of the United States - who must be a civilian - is also the Commander-in-Chief (CINC) of the U.S. Armed Forces. The idea is reinforced by such underpinnings as the law of posse comitatus, which states that the United States Military cannot be used or deployed against the citizens of the United States inside its borders. This is why the National Guard is used in disasters before federal troops; although the National Guard units are in fact units of the U.S. Armed Forces, they deploy at the sufferance of the Governor of their home state. They are, in fact, the 'well-armed militia' (hey, they got main battle tanks and jet fighters, what else do they need to earn the label) that the Constitution (IMHO) allows us to retain. This is true because instructions from their governor override those from the unified military chain of command (at least in theory).
Finally, the ability of Congress to legislate changes to the structure of the military itself reflect ultimate civilian control. For example, the United States Marine Corps (through probably the best lobbying of any of the services) is required by law to be two divisions (at least) in size. On the flip side, the requirement that Congress (eventually) approve any declaration of war (made by the President who is, after all, also a civilian) is an example of the limits imposed by civilian authority. | 
