China is unlikely to be a serious contender for world power. Its weaknesses are worse than our own, except they are hidden while ours are on the surface. China is much more likely to fall apart in the next few decades than is the USA.
Russia is in even worse shape, as is much of Europe.
That we are in a mess does not mean others aren’t in an even worse mess. You may recall how Japan, Inc. was going to take over the world, and fell apart economically shortly after this was proclaimed.
IMO
As for the US, things will only get worse until America defaults on its debt, sucks up the painful consequences, and then rebuilds, having learnt the harsh lesson of what happens when people and even nations live beyond their means... Of course, this also means that the dollar will have to forgo its position as the world's reserve currency, and the US will have to base its prosperity entirely on hard work and industry, rather than getting a free ride by printing out trillions of dollars to fulfill worldwide demand for dollars....
I don't know who. I don't know where. But I do know that the world has gone a long time without a big, serious war. I can hear a clock ticking.