[stripes1776]

The last thing China wants is a nuclear North Korea for the simple reason that it will force Japan to vastly increase its military capability and perhaps even develop nuclear weapons of their own, threatening China's entire regional supremacy.

Good point. Did the Chinese just now realize that? They could have prevented North Korea from developing a nuclear bomb, but for some reason, they didn't.

[maquiladora]

Probably just due to a growing realisation that China has less and less to gain from siding with a dinosaur like North Korea in the face of tempting Western economies.