There's an interesting segment in this psychology lecture about irrationality that seems related:
http://www.youtube.com/watch?v=i5IrSEIPdwk#t=44m36s
There is some advantage to being irrational, to having a temper.
Because if you have a temper and you're known to be irrational, people
are forced, by dint of your irrationality, to treat you better. Who am
I going to take from? The person who's extremely reasonable or the
person who has a hair-trigger temper? Well, I'm going to pick on a
reasonable person because the unreasonable person might do unreasonable
things. And this is faintly paradoxical, but often to be irrational, or
at least to have a reputation for mild irrationality, gives you an
edge.When someone calls your bluff, it's game over. Everything changes from that point forward. Either you can never act that way again, because people will know it's a bluff, or you freak out and do something terrible and then one way or another will be dealt with (police called, go to jail, get put on ignore, get an ass kicking, get nuked to complete annihilation, whatever).
The tragedy here is that America has subsidized North Korea's behavior and ability to exist. We're partially responsible for their regime thinking it can keep doing this, and naturally their threats have to escalate. Their bluff should have been called a very long time ago. It's like taking in someone bullying you, clothing him, feeding him, etc.
The key point is that this is really a proxy war between China and the US. North Korea exists only as a proxy of China - they cannot be defeated in war until China allows it, they will continue to exist as they do as long as China allows it, and the regime will collapse about 10 minutes after China stops supporting them. The current state of affairs exists because China likes having a thorn in our side and very much does not like having a close US ally on their border.
The only plausible end that I can see is them doing something so provocative that China gets fed up with them and afraid that they'll be drawn into a shooting war, and forces the Kim dynasty out and somebody who is reasonable and favors Chinese-style reforms in.
If you were just asking to be nice, I have a few old friends in South Korea (in the military, teaching, and local) but no family.
It is probably also worth noting that every single western nuclear power reserves the right to first use of nuclear weapons. In fact, the only countries who have ever adopted a no first use policy are the USSR/Russia (for 2 decades, but not any more), India (this is apparently more ambiguous now) and China (who continue to hold to it).
Wikipedia briefly mentions a North Korean pledge to the same effect, but I think this latest news shows that we should probably not take that too seriously.
The Soviets had always believed that the Americans wanted to attack them, perhaps understandably given that in the 1950s and early 1960s there were senior US military leaders who actually wanted to initiate a full nuclear war with the Soviets while the latter were still strategically weak.
The Soviets thought that the Americans were preparing a first strike during Able Archer and were preparing to preempt it - thankfully the exercise ended and everyone on the Soviet side calmed down and took their fingers off the button.
http://en.wikipedia.org/wiki/1983_Soviet_nuclear_false_alarm...
Nice to know that we came that close to annihilation twice in 1983.
http://www.imdb.com/title/tt0090163/
NB Threads, although it depicts an absolutely devastating attack on the UK (~90% dead within a few years), actually uses a rather optimistic attack plan - a real attack would actually have been far worse.
Dictator theatre is as much for the population being dominated as it is for the outside world.
Their economy is in the dumps, their people are starving, and they have gulags or worse throughout their country, so its not like the value other human life. Then back this attitude up with a large military which has access to conventional and other weapons, being next door to a rich and vibrant nation. Its not a good situation.
Until China decides North Korea is a danger to China and makes North Korea very aware they will take action to neutralize them North Korea will act with impunity.
The real threat to the US is that we cannot be one hundred percent sure what China will do if North Korea acts and we rush in to help South Korea.