A Chinese invasion of North Korea could be several things:
1) a preemptive action to avoid a second Korean War involving the United States, South Korea and possibly Japan against Pyonyang.
2) another step in China's Anschluss. They've already moved into Hong Kong and another renegade island. This could be a training prelude to an invasion of Taiwan.
3) a measure to see to it that China is the only regional nuclear power. A nuclear North Korea could lead to a nuclear South Korea and a rearmed and possibly nuclear Japan.
It is all three which China tries to achieve. This is a big move. China recently made waves on multiple fronts , which gave us enough clues to get some decent picture of what they are up to. I wonder how Americans reacts. So far they are quiet.
or Nkorea' getting ready to invade S Korea and China has N Korea's back!