First, those are their neighbors with which they have territorial disputes, like every other country (as borders where not there when the Earth was created, nor where they god given). Not some colonial grab, just out of pure greed, thousands of miles away, and with no prior provocation or history between the two countries.
Second, Mongols invaded and dominated China. You got your facts reversed. Ever heard of this guy, Genghis Khan?
Third, if we considered the same for the EU/US for example, we'd add the genocide of native americans, the abduction and slavery of 20+ million blacks for 4 centuries in the US South, colonial grabs and wars all over the planet (at some point 2/3rds of Earth were slaves under European colonial powers, not the inverse), tons of wars, the land grab of Mexico (California, Texas, etc), Hawaii, Phillipines, and Puerto Rico, the genocide of indigenous people of the Americas [1], and so on and so forth, plus 2 world wars, the genocide of the Jews, and the only atomic bombs to even fall (and on civillians).
Yeah, tell me again how bad China has been?
[1] https://en.wikipedia.org/wiki/Genocide_of_indigenous_peoples