Of course military action is an option now. It's a simple matter of who has more nukes... North-Korea could launch two, maybe three hiroshima-style nuclear bombs at South Korea, Japan, or the US. If they go for the latter, there's a good chance of them landing in the ocean. Also, if they do launch, there's a good chance of the nukes being shot down by Patriots and their kin.
The resulting backlash would be quick and dirty. No more North-Korea after that. It'd be blown to bits. Of course, you'd first get a conventional war before that, with millions of hungry North-Korean soldiers fighting their way into Seoul (if not nuked) and looting everything they can. They'd also get blown to bits eventually. In fact, they might not even make it that far - the initial NK bombardment will be intense, but their supplies will run out *very* quickly.
However... I believe China would take action long before this all would even happen. North-Korea with nukes is also a danger to China, and they do *not* like danger at their southern border - that's exactly the reason they want North-Korea there: to protect China's border!
North-Korea is going down, and everything they do seems to get them into more and more trouble. The US can just wait for the country to fall apart. The US *could* give in to NK's demands, but that'd be bad, and highly unlikely to happen.
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