

You have no idea if China did that. If they had, they would have taken great efforts to cover it up, and could very well have succeeded. It’s a small wonder we know any of the terrible things they did, such as the genocide they are actively engaging in right now.
There was organized violence deployed by groups of humans against other groups of humans long, long before anything we would recognize as warfare. Particularly brutal violence too, because the objective was not to conquer other people (something which only makes sense once agriculture is the dominant mode of sustinence), but to either drive off or exterminate a rival group so you can use their territory for yourself.
And we don’t even need to talk about people here: we have records of chimpanzees fighting small scale wars of harassment and extermination against neighboring groups.
Pre-modern, pre-civilization, pre-aggriculture, pre-you-name-it human life was far more violent than what we deal with today.