Considering both of those countries have nukes, the world would become a very grim place should that happen

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Seriously, China won't start dominating the world. As a state, their Goverment is very well placed, but it's people arn't. The Chinese people themselves won't ever have more GDP/person than an American would. Because in order for that to happen, China would have to become more service-sector orientated. And if that happened, where'd all the cheap goods to buy come from? China's income comes from the fact that the richer countries are very eager to buy from them, and if that deal went, all of China's new found wealth would dissipate.