Slate have a week-long, multi-part feature running, called How Is America Going To End?. It's half-depressing, half-amusing... and it's hard to tell how seriously they're actually taking themselves with this project (I'm going with Not Seriously At All). My favourite part is the interactive, Choose Your Own Apocalypse tool, where you can choose from any one of 144 potential causes of America's demise.
I'll take Decadence. (At least it's a fun way to go out...)
The story includes a linke to a list of reasons cited for the fall of Rome. Here I think I'll take one of the B's: backwardness in science, bankruptcy, barbarization, bastardization, blockage of land by large landholders, blood poisoning, bolshevization, bread and circuses, bureaucracy, byzantinism...