The USA faces a new threat of their own chosing: Terrorism
Yeah, some might argue that the "War against Terrorism" is simply an excuse to invade any country harboring terrorists (and strategic resources) or a ploy of the military industrial complex to keep the USA in an eternal war, but that's not the point. Let's assume that the USA wants to WIN for the purpose of this threat.
How can the USA win this war?
How can Terror bring the USA down to it's knees?
Winning conditions:
USA: All terrorist organizations either ceased to exist or ceased to attack US targets. Alternatively conquer the world.
Terrorists: The USA either breaks apart or loses the physical or financial capability of fighting conventional wars or loses all foreign military bases.
Everthing allowed, including nukes and genocide.
Have fun!