But what you said about likening the current situation to the fall of the roman empire is false IMHO. Such a superpower can't just live for only a few centuries except for a few circumstances ie a world apocalypse.
Your points are taken, and all very valid. However, with the acceleration of technology and overpopulation, things are happening faster. I do agree that if the US fall, it will be massive caos, or perhaps because of massive caos the US will fall. We can call it an apocalypse. I don't like that term though because it is so inherently related to the dumbest, most evil fairy tale ever told: The Bible.