I think US shouldn't freak out. US is very hypocritical, it pisses me off that I even live in this country. I mean, US has the most weapons because US expands their military power, constantly. US has the most nukes and the most nuclear wastes.
Also, Japan is freaking out because those few nukes can pretty much sink that island.
After all, Korea and Japan still have feuds amongst themselves. I don't care much about it, neither do my parents, but the gov't is the problem here. China..well, China always helped out N. Korea, but lately, it seems that they think N.K. is some psychotic country that they want nothing to do with.
Other than that, I think S.Korea is perfectly fine. They have one of the toughest military, and Korea will probably get aid from the US, probably Japan as wwell, and maybe other countries.
On the contrary, I think there might be a war...a small one, maybe. It's not as if their nukes and missles can reach the UK or France.