China and North Korea are traditionally seen together as allies, or at least neightbors that were mutually beneficial for each other over the decades. China has been the primary trading partner with North Korea, and is responsible for upholding the North Korean economy, purchasing a great deal of coal from the North Korean state. North Korea was a benefit to China as it provided a geological and geopolitical barrier between communist China and the US backed South Korean republics and Japan. However recent events have created waves in the diplomacy between the North Korean regime and the central government of China. How is their small traditional ally becoming such a prominent threat? Well, they are threatening the US, and have consistently pursued the means of transforming their threats into realistic possibilities. North Korea over the last several months has pursued nuclear technology, and a missile platform capable of striking Japan at least, the US west coast at most. This has created the necessity of the United states to respond to this threat. Such responses have become prevalent in the form of the THAAD anti ballistic missile defense system, the re-upping of US Naval presence in the South Pacific, and a renewal of support to the Japanese and indirectly to the Taiwanese in general. This goes contrary to what the Chinese need right now, as they desire to expand their influence in the Asia pacific regions. This becomes impossible with US military presence within the region. In order for China to reach its long term goals, they are beginning to realize that they will need to rein n the North Korean regimes, subsequently supporting US interests in the region in order to calm US military presence as well. By so doing, the Chinese will be better able to exert some of their interests in the region under a watchful US eye within the years to come.

Source: http://www.foxnews.com/politics/2017/04/06/chinas-xi-arrives-for-trump-summit-talks-expected-on-n-korea.html