Or maybe multiple powers will, as before WWII.
I think that is the most likely outcome really. There will be many strong players for a while, and that's actually a good thing.
rumborak
Yeah this seems the most likely to me.
I don't think anybody can just fill the American void in a fingersnap. I mean a lot of the reason the US controls so much of the world is remaining bases, etc. as a result of WWII and the Cold War, and rather than pulling back from these places when the conflict fizzled out, the US just stayed and continued exerting power and influence from those places - against Russia via remaining military bases in Europe, China via Japan/Guam/Pacific, the Middle East via Kuwait, Saudi Arabia, etc. So it seems like there would have to be some other major conflict like that with the same sort of aftermath for a country to actually end up dominating so much of the world within such a short timespan.
I think economically though, the EU will stay up there, at least relative to the other major powers. Europeans seem much less prone nowadays to military dominance.