According to the Economist a while back, once societies reach that level of decadence and corruption, they tend to implode. I personally suspect the US will go out with a whimper, not a bang, and it's already happening.

At least half of the richest nations on earth are in Asia, and while it's possible for us all to thrive, and peacefully coexist and prosper, the f- you attitude of crony capitalism is likely to end with a slow decline as things just get worse until people give up and stop buying so much tat.

So, less like the fall of Rome and more like modern-day Greece. I mean, Greece is fine, it's a lovely holiday spot, but it's no longer the centre of the world.