cofty:
One assessment I have read is that China (a) don't have a clue what to do about DPRK and (b) first and foremost don't want a unified Korea.
North Korea having ICMBs with nukes is not as such that bad for China for any reason I can see. I think the main problem from their perspective is that it might encourage others (Japan, South Korea) to get their own nukes and that may be undesirable, however, it is very unclear that will actually happen and China will, at any rate, remain the dominant force in the region.
If NK carry out another nuclear test - any day now - then China be forced to make a stand.
The question on my mind is why? China likely can't persuade North Korea from miniaturizing their existing nuclear arsenal (no success so far; unclear if real efforts are really being put into the problem actually) and when North Korea do succeed, what will China gain from altering its stance in that situation? I just don't see what is forcing China.
China may, in an ideal world, hope for a non-nuclear DPRK, but that has already happened and we got to think what makes sense for China right now and I think that is doing as little as possible.
NK must be prevented from having nuclear weapons at any cost but that cost might be massive.
What are the real options here? Draw a line in the sand and wait for north Korea to cross it, which they will?
According to experts in North Korea (actual experts, not talking heads on TV) it is very likely DPRK may evaluate the situation from a completely different set of assumptions than we assume. I recommend "The cleanest race"
Imagine after the first bombing run hundreds of thousands of NK troops pour into the northern provinces of south korea which is what they have prepared for decades... will there really be a political will to push them back considering the conflict will be fought with chemical and biological weapons in regions already devastated by shelling? will it be possible to actually defeat DPRK or will China prevent than by threatening to step into the conflict (i.e. a replay of the Korean conflict?).
I think it is easy to imagine that DPRK believes they can win such a conflict (i.e. inflict damage on south Korea, possibly moving the border slightly south), which would make sense of why they seem to make threats of war nonstop.