The Chinese believe most of all of Siberia should belong to them and they were screwed out of it in an unfair treaty about 100 years ago.
The Chinese belief they should own Siberia is on a par with their belief they should own Taiwan. You just don't hear about it as much.
The Chinese and Soviet Union duked it out in vicious, fairly large scale ground combat over some border areas in the 1960s. There were no reporters there to film it, and both countries suppressed the knowledge that it happened.