The Chinese have been planning to intervene in North Korea for a long time. Richard Fisher of the International Assessment and Strategy Center points out that the Chinese military has been modernizing along two principle axes, one of them being the route between Beijing and Pyongyang. “Today the Shenyang Military Region next to North Korea has the most modern mechanized army systems and can call on enormous air and missile forces,” Fisher notes. “It is likely that China is far more ready than the United States to wage the next Korean War.”

In the past, Chinese civilians and military officers were unwilling to talk with outsiders about military intervention. That changed, and a few years back military officers began laying out their plans to move into the North in the event of crisis. Glyn Davies, then America’s chief nuclear envoy, in May 2014 publicly said the U.S. and China were in discussions about “all kinds of contingencies” regarding the peninsula. Davies’s unprecedented disclosure came in response to a reporter’s question about claims by Kyodo News that it had obtained a copy of a Chinese contingency plan for the collapse of the Kim regime.

Kim Jong Un’s generals obviously think the Chinese might move on them. The Korean People’s Army last year reportedly transferred 80 tanks to its newly formed 12th Corps, stationed in Ryanggang province close to China, and had plans to send another 80 armored vehicles. The corps was formed to defend against a Chinese invasion, and the movement of tanks is believed to be the first deployment of heavy armor to the area.