Kim Jong Un doesn't want to become the poorest province in China. He has signaled this objective very forcefully by eliminating his mentor and uncle, Jang Song Thaek:
Jang's fall from grace, accompanied by allegations from corruption to womanizing and capped by his dramatic arrest at a party meeting Sunday, has no doubt spooked Pyongyang's elite. It also suggests Kim is still trying to consolidate the power he inherited from his father two years ago.
Why was Jang targeted?
In 2012, he led a business delegation to China to discuss the construction of special economic zones.
And those aligned with Jang are being purged, too, it seems.
Strategypage summarizes this nicely:
If North Korea collapses China has a problem and North Korea gets more unstable with every passing year. The most recent problem was the very public, dismissal of the uncle of 30 year old North Korean leader Kim Jong Un. The uncle (Jang Sung Taek, who is married to the sister of Kim Jong Uns father) was purged for corruption but also because the Jang was seen as too cozy with China. Jang was a key Chinese asset in its attempt to get the North Koreans to reform their economy. But Jang overplayed his hand and is now under arrest.
Now the pro-China faction is under pressure to conform to Kim Jong Un's wishes or face the consequences. And Kim Jong Un wishes to be the biggest fish in a small pond no matter how much evaporation is taking place, rather than becoming a local ruler of a tiny, impoverished province of the Chinese empire. For the preservation of his own relative girth, that's probably wise. The entire country suffers (minus the few percent who can enjoy the things Jang was arrested for enjoying), but whatever.
So China will have to consider how to rebuild their faction, hoping that it can regenerate before North Korea collapses and risks South Korean (and America behind them) intervention to prevent a humanitarian disaster--which puts South Korean troops on the Yalu.
And if that doesn't happen? Well, there's Plan B of invading along a road network that China is helping to create in North Korea:
So if there is a dispute among the powers about who should administer a collapsed North Korean state, China is making sure that the main highway into North Korea allows the Chinese army to rapidly drive south to Pyongyang.
And from there, the Chinese army can fan out to other parts of North Korea to various provincial capitals.
And I suppose getting the South Koreans agitated about their southern flank by announcing an air defense identification zone that overlaps South Korean sea claims is all part of the effort to keep South Korea from focusing too hard on the problems of moving north across the DMZ.
