China right now has little power projection ability, and invading anywhere would likely start a very costly war with the US. If China had the same global military dominance as the US does now, it would be much, much more aggressive. It openly wants to outright conquer Taiwan, just for starters. There's a whole Wikipedia category on Chinese border disputes:
Now we're getting somewhere. I agree, China likely isn't doing so because they lack the power. Same way, the USG isn't putting people into re-education camps largely because the people won't let it do so.
If you want to limit the ability of superpowers to kill millions with impunity, then really the best solution is to have a bipolar world.
https://en.wikipedia.org/wiki/Category:Territorial_disputes_...