I’m sure you’ve seen this article by Orson Scott Card on Korea – it’s all over the blogosphere, although I found it via Glenn Reynolds. I think it’s a pretty good analysis, although I don’t think China is going to publicly put North Korea under its nuclear umbrella. I’m not sure what form the guarantee will take, but I think it will more likely be a treaty or agreement that includes China. The important thing to remember, as this article points out, not everything that happens happens in public, and not everything that can be said should be (or is) said in public.
I thought this article (in the NYT of all places) makes a fine companion piece. North Korea is a drain on China — it exports refuges and imports food, money, and resources. South Korea is an asset to China – both as a market (third largest trading partner)and as a source of investment (fifth largest foreign investor), and I’m sure that comes with some technology transfer. In a sense, both South Korea and China would just as soon North Korea disappeared from the map, or failing that, the status quo is just fine, thank you very much. I doubt South Korea wants to try to unify with the North after the example of German reunification, and China is stuck for reasons of history and status with being its protector. So for the Chinese, any problems North Korea causes the US is OK with them; to the extent North Korea causes them problems, well, now something has to be done.