China's one child policy has created a massive cliff in their demography. A generation later, there aren't that many children to take over from and support their parents as they move out of the working population. While industrial capacity can be made up for a bit with automation, which china is investing heavily in, the common people will still see economic hardship. Further, the one child policy led to an extreme skewing of the sex ratio, which means large numbers of males will not be able to find partners in china. The wealthier ones will emigrate, taking their wealth with them, while the poorer ones will be left with nothing and no one to lose in a country whose interests become increasingly misaligned with theirs.
For the moment, large numbers of people still remember when china was weak, and from these ranks come the party leaders who staunchly defend and promote national unity. These people will die off in the not too distant future though, leaving people who never had to live through the bad times which justified the communist government's existence. Much like how the soviet union collapsed as soon as the tsarist age passed out of living memory, china will struggle to convince the disparate parts of china are stronger together as their growth slows and totalitarian policies become ever more divorced from real threats.
Unified chinese states have formed many times in history. They have also shattered many times. The actions in recent years of putting economic growth above all else, suppressing ethnic minorities in favor of a homogeneous Han state, and building up institutions for societal control are not the actions of a powerful emerging superpower but desperate ploys to stop history from repeating itself before it's too late. While perhaps they will succeed, at least for some time, I personally think the next few decades will not be kind to china.
America and the west would be better served making sure they don't succumb to similar problems. Europe likewise has an inverted population pyramid and the horrors of world war 2 which forged the west's present unity is likewise about to pass out of living memory. The west is at least much more open to immigration than China so it has less resistance on the path to fixing its demographic problems (despite the rise of recent alt-right/anti-immigration movements). Further, the west's unity formed from many organic interconnections of economic and military shared interest rather than being forced upon it by a central authority, so those bonds are presumably more resilient. That said, the west is much more indebted and its power much more overextended in places like the middle east and africa. Its challenges will be different in nature but similar in degree.
The world is likely to take a very surprising form in the not too distant future regardless of any attempts to shape it.