Let us look back at history of Roman Empire,it didn't fall bcoz of a superpower enemy but because of it's own weight and in hands of tribes and nomads.Today US is also suffering in hands of a bunch of rag tag Middle Eastern freedom fighter guerrillas.And it's economy is in shambles thanks to it's corporate houses' economic greed and bcoz of it's churches propagation of hate which is causing war and bcoz of which so many young US men are returning home with one leg or one hand.
All empires rises, thrives,and perishes.