Make North Korea a Chinese Protectorate
During the Cold War, the Warsaw Pact nations were Soviet protectorates. What that means is that nations like East Germany have a degree of nominal independence, but their foreign policy and national security positions had to strictly conform to the interests of the Soviet Union. Rather than annex the nations of Eastern Europe after the Second World War, the Soviets made these nations protectorates.
The Soviet Union took responsibility for the actions of these nations. So despite the fact that there were many theater nuclear weapons with effective delivery systems in these nations, these could never be used without the consent of the Politburo. NATO never had to worry that a rogue leader of one of these nations would threaten Western Europe because every leader of a Warsaw Pact nation was ultimately under the control of Moscow.
America ought to take the position that North Korea is a protectorate of China, recognizing China's right to represent North Korea's interests in global affairs and also to recognize that China can take whatever action it deems necessary to restrain North Korea. That places both responsibility and authority to Beijing.
What that would mean is that if China occupies all or part of North Korea, or, indeed, if China annexes North Korea, we would accept that decision without negative comment or action. It would also mean that if North Korea launched any nuclear attack against Seoul or Tokyo, then we would consider that an act by China against South Korea or Japan.
America, under this arrangement, could give food and other aid to North Korea, but only through China. That would give China extra leverage in dealing with its new protectorate. The affluent democracies threatened today by the madman in North Korea could give every deference and support to China in controlling North Korea.
Why might China want the privilege and the burden of accepting North Korea as a protectorate? China's authority would be formally expanded, something Chinese expansion into the South China Sea suggests that Beijing would like. China also could act to prevent a nuclear attack, which would throw global markets, Pacific trade, and financial markets into a calamitous death spiral – a disaster that would hurt China as much as any nation.
North Korea might also view this favorably if China then ensured the rule of Kim Jong-un, the dominance of the Communist Party in North Korea, and the safety of that nation from any foreign attack. The dubious capacity of North Korea to attack America if America threatened that regime would be replaced by the very real power of China to hit American cities.
The system of protectorates seems archaic and a throwback to 19th-century imperialism, but in fact, protectorates work. The client state (the state over which a protectorate is made) gets the protection of a great power, the great power gains influence and control, and the rest of the world has a more responsible nation superintend the actions of a smaller, potentially rogue nation.
How might this protectorate status be created in a way in which the international community would be compelled to take notice? Here, for once, that most useless creature of modern international politics might be actually helpful: the United Nations, and particularly the Security Council. A vote of that body placing North Korea under the protection (as a protectorate) of China would reflect a global concern about the threat North Korea poses today, and it would make it almost impossible for North Korea to do anything but accept this status.
This protectorate would also allow a gradual evolution of North Korea from the sort of malignant insane asylum it is today into the sort of regime that exists in China today, a hardly ideal but vastly less malign and much more rational nation. This would allow South Koreans to re-establish contact with North Korea, without reunification, and it would evolve North Korea into a nation with a stake in peace as the economy of North Korea grew slowly into the sort of quasi-market economy of China.
There are few, if any, truly "good" solutions to the nightmare of North Korea. Creating a Chinese protectorate is the best solution to a horrible problem.