There is only one country that can simply and unilaterally force North Korea to abandon its nuclear programme: China.
So the question is, why would they?
China has a number of traditional enemies: countries it doesn't trust. One of them - India - already has nuclear weapons. Japan does not, and China would do a lot to prevent Japan acquiring them.
The novelist David Baldacci - through one of his fictional characters - has suggested that the US simply needs to say to China "sort out North Korea, or we will help Japan acquire nuclear weapons". A blunt ultimatum like that would probably not work with the Chinese. They don't react well to threats, and cannot be seen to back down. But you can achieve the same thing more subtly.
For example, if Japan were to announce that, because of the threat from North Korea, it is thinking of renouncing the Nuclear Non-proliferation Treaty, this would certainly concern the Chinese. They would probably ask the US to prevent this. To which the US could respond that, in the light of North Korea's behaviour, the Japanese position is understandable.
How long before China forced North Korea to abandon its programme?
