The relationship between the D.P.R.K. and China is close and will remain so despite U.S. efforts to isolate North Korea yet cynically use China to advance U.S. interests on the Korean Peninsula. The U.S. should not expect the D.P.R.K and China to split apart. They need each other. They see the U.S. as a threat. The D.P.R.K represents a huge refugee problem for China should it destabilise and far apart. The trade between them is large by North Korean standards. Both China and the D.P.R.K have strained relations with Japan which is a virtual U.S. colony in terms of foreign and military matters. The U.S. does not understand the history or the geopolitical realities of Sino-Korean relations. They both feel lingering hostility toward Japan due to its expansionism in World War II. They are both threatened by America which creates further rapprochement. They are both socialist states but with widely differing economic structures and outcomes. They are Asian.
The flags of the Democratic People's Republic of Korea and China.
The bilateral relationship between China and the D.P.R.K has deep roots. During the Korean War which began in 1950 the opposing forces surged up and down the peninsula: and at one point the communists of North Korea had advanced as far south as Pusan. Then there were counterattacks and U.S. forces and the South Koreans surged up to the Chinese border as it raced across North Korea. In October 1950 with American forces at their door at the Yalu River and the arrogant, warmonger General Douglas MacArthur talking about invading China by bombing their bases in Manchuria—he was eventually relieved of his command in April 1951—Chinese military units entered the Korean War. Chinese military forces crossed the border and joined the North Koreans as they liberated Pyongyang in December 1950 and drove U.S. imperialist forces (an appropriate term even though fighting under U.N. Security Council auspices) and the South Koreans back across the 38th parallel retaking Seoul.
The D.P.R.K is deeply grateful for the Chinese support in the war which killed some 3 million Koreans, left 1 million homeless, a million Chinese dead and 35,000 Americans K.I.A. An armistice was signed in June 1953 which was more of a cease-fire line and not a peace treaty or a formal end to the war.
It is not ironic that the only foreign power to have a significant troop presence in East Asia is the U.S. Japan's Greater East Asia Co-Prosperity Sphere was their not very subtle description of their thirst for empire during the war. Australia is an episodic occupying power in East Timor but for much of Asia, they see the U.S. as the "successor state" to Japanese expansionism. It is clear to me that the American military presence in Northeast Asia is very destabilizing. Even Pat Buchanan has called for the removal of U.S. forces from the Korean Peninsula in the event of D.P.R.K. military escalation across the DMZ!!