Most people agree that North Korea is a problem. Aside from its nuclear tests, it also stands accused of state-sponsored counterfeiting of foreign currencies, the industrial-scale manufacture and sale of illicit drugs, and even of assassinating its own citizens in foreign countries.
But why is North Korea China's problem in particular? China is North Korea's only major diplomatic ally, but the relationship is fraught with difficulties. How did China get saddled with such a troublesome partner? The history of the relationship runs much deeper than most people realise.