No one asked the Chinese natives originally there if they wanted to separate from China.

Ok, but has anyone asked them anything now?

IMO it wasn't a good reason to fight a civil war. Fighting to force the south to end slavery was a good reason. Or because the south attacked the north because what it really wanted was to force the north to obey their laws about returning slaves rather than just secede and do their separate thing.

But the whole "you belong to us, like it or not" attitude is just imperialistic evil whether done by the USA or China. Or Russia or Israel.

Like if Texas seceded, the only military intervention I'd agree with is one that ensures those who don't want to be a part of separatist Texas have free passage out and support for areas that want to secede from the independent Texas (and both of those are under the assumption that Texas is gonna Texas and try to oppress/put down those people instead of let them do their thing). And there would probably need to be some kind of treaty that figures out how to handle the federal stuff in Texas and it would be incredibly complicated, but I don't think "it's complicated" is a good justification to civil war them into staying because it's already there.