... and send them back to the stone ages!
Wouldn't take much...
The reason we don't, though, is that China is bound by treaty to defend N. Korea from any attack.
This is something we haven't seen for a while: a classic cold war-style standoff.
The difference is that we aren't really that concerned about China and aren't trying to kick Communist Butt in N. Korea. Our goals - on the surface of it, at least - seems to be to keep N. Korea from pursuing its nuclear program any further. That would destabilize things too much for our interests.
N. Korea still has FAR more to gain from ~having~ a nuclear weapon than it does from using it. I'm not sure what they will DO with their state of war declaration, but I don't yet see how actually going to war will benefit them.
The trick we have is defending S. Korea - which is our obligation by treaty - without attacking N. Korea directly - which might force China's engagement. If S. Korean troops attack N. Korea then China will have to engage. Simplest thing, and the most expedient for us diplomatically, is to be ready to defend the border and crush any invasions in to S. Korea.
N. Korea likes to think it can attack the US. It ~might~ but doing so would bring the Hammer of the Gods down upon them without mercy and the world, largely, would approve. Doing so might also nullify the defense treaty with China. From what I understand China isn't all that keen to defend N. Korea and is more interested in preserving the peace along its border. China's current troop concentration near N. Korea seems more about keeping the conflict from spilling out into China than it is an expression of willingness to co-invade S. Korea.
So N. Korea has a lot to gain from making lots of noise but relatively little to gain from actual aggression.
As for the poll... I always have a fair amount of supplies on hand and things like this don't spur me to buy more of that kind of stuff. I buy more when I've consumed too much and need to restock. Its just prudence here and not paranoia.