Gangsters joining the military to receive combat training has motivated them since I was a cop, so it's not a recent problem. In fact, not all that long ago I watched a TV clip of gangsters assaulting cops using military tactics.
I might be wrong here, but I do believe that the Black Panthers was the first gang to train extensively using military-type tactics. It makes sense because it was the first gang of which I'm aware that had as its primary objective the overthrow of the US government. In essence, they were preparing for war.
