That's easy. Since the end of World War II, all of them, in equal measure. That's what the Military-Industrial Complex is all about, Charlie Brown. It has nothing whatsoever to do with the defense or the protection of the American people themselves. Never has been.
I can only hope that Rand Paul's question was a rhetorical one. Otherwise, he really is as big a fool as I suspect he is.
No, to ann extent it eas justified during the Cold War. Then it should have stopped. The Cold War came home.