> But historically, China has never been good at ruling non-Han peoples.

"Good" is not a very objective term, but China does have 55 official minorities, coming from a long period of imperial expansion, so arguably it can be done.

> The Chinese way of thinking is that only after a group has been fully Sinicized (language, culture, identity) can they be considered “one of us.”

Firstly, this is a troubling statement, again given that China has 55 official minorities, who are evidently failures of assimilation more than anything.

Secondly, there are other ways of imperial sovereignty: Vietnam was a Chinese dominion for a longest time, and Korea was effectively ruled from China as well.

In other words, China has a long and not very remote history of territorial expansion and old-school dependent-state imperialism. The fact that the Han have a very strong cultural identity and do not find it easy to coexist with other peoples doesn't help either: just look at the history of the relations between Britain and Ireland.