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The consensus is that China’s prime interest is stability. The survival of the Kim dynasty ruling North Korea now seems bound up with its nuclear programme. So China may think that stepping up efforts to shut that down would not be in its interest. Certainly many Chinese scholars and, presumably, officials feel exasperated with North Korea and rather embarrassed by its antics. But China fears that collapse of the regime might lead to unrest, refugees crossing into China and the presence of American forces on the other side of China’s own borders. That would be even worse.