Rome and America share a plethora of similarities. In my opinion, America may end in much the same way Rome did. Rome was the strongest power in the world only to be wiped out by mere Barbarians. There are many reasons why Rome, like America, was flawed and corrupt.
Rome fell because it created an empire so large that it simply couldn't support itself the way it could in earlier times. Barbarians overrun it because A) Soldiers could not be mobilised fast enough to combat the threat B) The ones that could didn't stand a chance against the superior numbers of the barbarians, regardless of how well trained the Romans were and C) Almost all of the land conquered by Rome was taken from the natives by force, so the natives did nothing as the empire burned. America meanwhile doesn't invade other nations, it merely spreads its influence to them and encourages them to do what America wants. America is also one of the most technologically advanced nations in the world and so can afford to have a large "unofficial empire".