The areas of Siberia bordering Mongolia and China are quite remarkably like Mongolia and China, rich in minerals, timber and quite a bit of fossil fuels. All of which China covets. It's going to be the hot spot in Asia in the next decade, in my estimation.
They are not all ethnic Chinese. We think of China as this homogeneous people but they are not. In 20 years China may become the domain of dozens of various warlords when the Red Chinese communist dictatorship falls. like it was a 100 years go.
In my thinking, China is not an expansionist land power per say but an influence expanding regime that goes back to when the emperors thought themselves the center of the universe and all nations needed to come to China and kowtow to the emperor. The Chinese burned their fleets after they sent them out to span the known world to awe the barbarians. The Europeans are different - they send fleets and directly occupy or conquer. The Chinese in history did not really do that.