Kevin -- I don't think a scenario like the Roman empire's collapse is totally applicable, although it's instructive. The world today is far more interdependant than it was then, and the pace of events much faster. It's hard to imagine the same kind of lengthy power vacuum in the wake of the Roman empire's collapse when a military threat can be mounted in terms of days instead of years. *Someone* would manage to take up the slack in a very short period of time, IMO.

But if there is an equivalent to the barbarians, it would probably be multinational corporations, plundering national resources because they are not carefully guarded by the nations. In our generation, the corporate barbarians are taking over the government by intergration instead of conquest.