It's not so much that China is going to be the lone superpower - it's going to be more of a multi-polar world again as the US is still light years ahead at least in terms of military tech.
The US will eventually decline economically relative to China, but the US has other advantages, besides military tech. The US has exported its political model to Western Europe over the past 100 years. A lot of middle-class people in China want to live in the US, Canada, Australia, and Europe, and will do so as fast as those countries let them in. The English-speaking countries will let them in the quickest, perhaps to buy those empty houses. Such emigration out of China, coupled with their one-child policy, means China will hit a demographic wall quicker than Japan ever did.
And of course, because of Western countries' tradition of federation and democracy, the US and Canada can slowly merge with the EU, treaty by treaty, just as fast as it needs to to counterbalance China. NATO is just the beginning of this. I'd imagine Russia will eventually, perhaps in 20 or 30 yrs, join the EU, Euro, and even the Schengen zone one day. Such a combined US/Canada & EU/Russia would have well over a billion people, with most people probably speaking English, and be centred around the Arctic Ocean, which by then would be the best land on the planet because of climate change.
But who's China going to federate with? They've had trouble keeping their Western provinces in check, and keeping their own people inside the country. They'll probably get Mongolia, maybe even Burma, within 50 yrs, but none of their other neighbors will trust them enough to let them too close. Russia will look to Europe to help defend its Siberian resources before it lets China in. Perhaps their immigrants to the West will stay loyal as part-time spies, but their children certainly won't.
In 50 yrs, a combined US/EU/Russia will be top dog, with China lagging in 2nd place, and Japan, India, Brazil, in the third tier.
You reckon? Who do you suppose gets the most bang for their military buck? Who's got the bigger manufacturing base, which is what all big wars come down to in the end?
The USA still has the superior military, yes. But even now, it would be a very nasty fight indeed. In ten years' time, when China has handsomely exceeded the ship numbers of the US Navy, it's anyone's guess who would win, and let's hope we never have to find out.
