Balkanization. Probably what China is hoping for anyways so that once the world's hegemon finally keels over and dies they can take over (So they think). Likely it will be Russia or a stronger European country moving in to fill the gap.
Russia's demographics are even more fucked than China's. Their aggresive behavior is not coming out of strength, but, like China, out of weakness. They know they only have a few more years to secure their borders before their aging crushes them. After America, there won't be a world hegemon, not even a bipolar world between America and China. It will be back to a multipolar world with, in my opinion, the following countries being the main powers:
America: Will still be a world power due to their navy and the fact that they're a strong country in an entire continent of weaklings. However, they will only be interested in the Atlantic and Pacific, keeping Japan, Australia, and parts of Europe as allies, while keeping their alliance with Mexico to secure the southern border. If Mexico becomes more prosperous, it serves the USA in the end.
Turkey: The most stable nation in the ME (yes, even with Erdogan) that has industrialized and preaches a non-extremist version of Islam. As Pan-Arabism fails, Turkey has a great chance to reform their Ottoman holdings, even if it's more influence than territory. A lot of the Balkans will also fall under their influence.
Iran: This will only happen if they get rid of the mullahs and dig back to their more tolerant Persian roots, but if they do, they basically can control the Eastern part of the ME. Relatively stable for the area, with an clear tradition that goes beyond Shia extremism and borders that makes sense.
France: Probably the only country in Europe that doesn't have an incoming demographic collapse and has a military that actually works. (They're the only military that doesn't allow women in the front lines in all of Western Europe, which is how you know they are a serious military). They have actual monetary influence over most of western Africa and can pull Spain and Italy into their sphere of influence. No other European nation can really compete. Germany is aging at the speed of light and will not be able to maintain the EU and the UK is basically going to become an American puppet post-Brexit just to be able to kept under American naval protection.
Some unknown western African nation: My guess would be Ethiopia, being one of the advanced nations that is industralizing in the area and one that is currently damming the Nile and can project that influence into Sudan and Egypt. They just need to fix their current social issues.
East Asia is way too fucked to predict. China has an incoming demographic collapse but the other potential power, India, has way too many internal problems. It's a toss up between those two in the mainland. Japan, if they can somehow fix their demographics, still has the best navy in the area, second only to the US navy.