Simply to keep power, Kevin. North Korea is and has been for a long time in the grip of famine -- WHO and other international agencies agree that hunger and malnutrition are tremendous problems there, THE country's problem, in fact. Yes, NK rattles the nuclear saber and other countries jump. But I would have no surprise if the US decided not to play any more and talked Japan and South Korea into going along. When people get hungry enough they don't care who is behind the machine guns they face -- survival is paramount. Should that point loom, I think that the NK rulers would jump the Z rather than abdicate.

Unless China took care of the matter first, and it very well might. The Chinese leadership aren't fools; they are very aware of the fire the atomic match would light in Asia. It would NOT be good for business, and China, in spite of the words, is now a capitalist country run by pragmatists.