Let’s think about China and North Korea, because that is the dynamic that matters here when thinking about the NK threat/crisis. Put simply, China has clearly made the decision that the possibility of a unified Korea is a much bigger problem for them than the thought of North Korea as a nuclear power. Possibly they justify this irresponsible behavior by thinking a nuked up North Korea can be ‘contained’ and therefore the threat is overstated, possibly they justify it by claiming all great powers act in their own interests and view any change to the despotic NK regime would amount to a threat to their own despotic regime - North Koreans being freed from tyranny no matter how chaotic that process might be would eventually for China prove a bad example for its own people to contemplate and maybe envy. For China, protecting the status quo in North Korea is all about protecting the status quo of one party rule in China and keeping a unified Korea and the American military presence that would come with it from its border.
Here’s the problem about that for China - believing you can put off in perpetuity NK morphing into a serious problem re China’s national interests is based on notion that eventually America will simply learn to live with the threat - but what if the US decides that they simply cannot accept the threat, which is certainly what I believe to be the case? Then China refusing to take significant actions to shutter the NK nuclear program would necessarily lead to significant US actions - of which I think there are only two types, both of which eventually lead to the use of force. One, robust increases in both American ABM assets in the area and an American military presence overall ending in the US ultimately having to commit to intercepting NK missile tests; or two, a larger use of force - beginning first with sanctions and some sort of blockade of NK, putting China in a very difficult position - graduating then to targeted strikes on NK missile tests - and finally to a massive strike or at least the very credible threat of a strike on the NK military - and absolutely no one, especially the Chinese, wanna see that.
Logically, it seems to me, when it comes to how China currently sees its national interests, which is all about preserving the status quo of one party rule and preventing a unified Korea, then no matter what happens in North Korea is bad for them if you believe the US simply cannot allow NK to become a nuclear power. Given that’s the case here the questions become - can you convince China of this reality and what’s the next step if you can - in other words, what’s the next step if China becomes an active partner with America and its allies in closing down the North Korean nuke program? I’m guessing that would depend on whether or not China has a plan to stage a coup in NK and just as importantly contacts with elements within the regime to bring such a thing about. Now, clearly given how China currently views its national interests it really doesn't wanna be doing something like that - but we’re working with the assumption that you’ve managed to convince China that its national interests are going to take a hit no matter what - and if so a coup becomes the best option, even better than Kim simply backing down since he could never be trusted to abide by any agreement - although China would obviously prefer Kim simply backing down. If China hasn’t nurtured the wherewithal to stage a coup, then I think the only option becomes bringing one about by completely shutting down the NK economy - a much more dangerous scenario since, if a coup fails to materialise, war becomes probably inevitable - and then it will all be about how successful the US and its allies are at making it a short one.
Again, how one views this problem is entirely dependent on whether you believe America can or cannot live with a nuked up North Korea. Clearly, with Obama, China could safely believe in America doing nothing serious about the threat - but I think that calculation no longer applies with the national security team Trump has put together - I think moves made by Mattis et al point to a much more reliably hardline foreign policy. Yes, if that’s true, weakness or general mismanagement and irresolution from Trump can completely erase those hardlines and no doubt China will try and drag its feet as much as possible while it figures this potentiality out - but right now my guess is that as long as Mattis et al seem to be handing him ‘successes’ Trump will give them a lot of leeway re standing up a strategy going forward.
[the recent failed launch of a test missile along with another failure not long ago raises another angle to the debate over North Korea - namely, what if the US has developed the ability to use cyber weapons against NK’s nuclear infrastructure? Certainly, this is entirely possible - it’s just that I’ve not yet read from a source I trust a credible case for it. But if we assume it’s true, the problem I have with it is that I wouldn't see it as a long term solution - great short term payoff - but long term no - although I might change my mind about that once I read something that credibly lays out how that approach would work. I mean, even if it is true I assume there are countermeasures and probably pretty effective ones that NK can roll out - hell, Stuxnet was a pretty sophisticated cyber weapon and it fell short of its hoped for potential - so count me at the moment dubious about the merits of this]