You absolutely should remember the Chinese war with the first of those; if you have trouble, a good way to remind yourself is that it was not long after the US one.

Tibet, Manchuria, it should be somewhat obvious that a nation that is as ethnically diverse as China was not a nation borne out of lots of different people deciding simultaneously that they would like to create a country together.

What is modern China has only existed for 100 years or so. When the country collapsed there were ethnic divisions that were erased after the country was unified.

The hallmark of successful ethnic cleansing is people claiming that there were never any wars, that things were always this way. The same is true of Kaliningrad, the most German city, centuries of history as a leading nation within Germany and the HRE, now a completely Russian city. It is only in the West that you see any narrative around division, in places like China or Russia history is erased (and how could it be any other way, the cornerstone of Chinese politics is one nation, one people...there is no political value in this narrative in Western countries).

It certainly wasn't a denial. China could learn a lot from that.