Personally, I think US power is already crumbling. The death rattles started some time ago. All world powers eventually die, and a lot of the rhetoric about trying to maintain or increase our power that we have been hearing in the last 10 years seems to be the surest sign that our foundation of power isn't very strong.

IMO it's possible that the US might split into two parts -- CA and the southwest with maybe NV, OR and WA along -- but I don't see it as likely anytime soon. The most likely scenario for such a split to me would have to be led by California, but I doubt that the other states who might philosophically join such a split would be content to let CA rule them. The probable structure would seem to me to be, at least at first, a confederacy of states with a separate joint "federal" government; much along the lines of the early US when there were strong states rights.

I tend to support such a split in theory, because I don't think that the US federal government begins to adequately represent the varying needs of this large and diverse country. I think the US would have to lose it's position as a world power first, I think, before there would be an internal split. Any split prior to that would be not only nearly impossible, but very damaging to relations. And although I meet many people who support an independant California, none of them would like to see anything other than close, friendly ties with the rest of the US.

We won't see any significant change in the world political situation that recognizes the US as the world power until there's another country or faction that is clearly the replacement. Is it a united Europe? Maybe if they can stop squabbling amongst themselves.

However, I'd venture to guess that China may be the next potential world power, but not for another 20 years or so.