hah thanks for the invitation to babble freely I read about this stuff like some others might read celebrity news, and it's so rare that I get to see a conversation on here about it.
As others have noticed, it does (again, my opinion) comes down to economics. We want to believe countries don't want to go to war because it's horrible and people die. The problem with NK is they have people dying, people are so desperate as to turn to cannibalism in many areas, it is a wretched and heartbreaking situation in that country. South Korea flourishes and it angers their government. The government has spent what very little money they have on developing missles and testing them. They don't have a lot to lose at this point.
KJI has spent his life having smoke blown up his ass; I don't know if he believes what he says or not. He's not out there with the people; he's fat and happy, and evidently, crazy. His father sabre-rattled a few years back and it did earn them some more money for food from international aid. The government could easily have trade restrictions lifted or eased simply by changing their policies on nuclear research or human rights.
More on the nuclear research: I realise some have disagreed or mentioned negatively the idea that only certain countries seem 'allowed' to have nuclear programs, however, NK is a very good example of why this happens. If we had free trade, free flow of information between nuclear nations and NK, they'd be capable of so much more already. The lack of trade keeps them from having the money to spend on these programs, which are expensive. Their government has proven time and again it is not capable of managing nuclear arms without flying off the handle every few years and threatening us with them. It is not an ideal situation because of the human rights abuses they subject their people to, however I am not sure the people wouldn't be suffering regardless of trade, as most of the money seems to go directly to a corrupt government and their military program.
I hope my opinion on the US aspect comes out as neutral, but obviously I am from the US originally so I'll put that out there in case you want that grain of salt to take it with. However, as warmongering as we come off in certain situations, say when oil is involved, the government doesn't want another theatre of war right now. We don't have the manpower to sustain yet another war, and we certainly don't have the popular support for it. There is no oil, no hidden reason (that I know of) for us to want to take on NK. We've been dancing around them diplomatically for years now. We keep bases in South Korea but mostly because of their proximity to what we might call real threats. We don't know what China is doing, and it's closer to (for example) Afganistan than the mainland US. We need bases to mobilise quickly if we're needed.
(I get it, Team America world police. I saw the film and I laughed, I promise. But at the end of the day, the American military is the one people assume will Do Something, and it's hard to Do Something from thousands of miles away. Hence the need for bases for gear and troops)
So for once, I can't agree that the US wants to go to war. Not for this one. There are only drawbacks: real potential for creating a foe in China, involving more troops we literally do not have as we still have them in Iraq, Afganistan, etc. These fears were articulated a year or two ago when we were afraid Iran was going to kick off; lack of troops.
China won't want to go to war, either. They're currently, as usual, pissed off at Japan, and are doing most of their posturing over some islands they're arguing over at the moment. I admit, that actually worries me, because Japan is a close ally of the US. I digress.
At the end of the day, their missiles are terrible and unable to reach very far. When I bring up bases, this is another reason for them: NK has no bases anywhere. If they were to launch an attack, it would have to be from NK soil. They simply don't have the range to reach anywhere near us (adding all of that for those who sounded worried!) Last I knew during their previous round of missile testing, they could reach Darwin, Australia in a pinch. That might have changed, but that's the sort of range in terms of our immediate allies. And I'm not sure if I've said it in this ramble, but their longest-range missiles were unable to carry nuclear warheads, last I knew.
Most important in all of this is the reactions from nations which are rather good at sabre-rattling, themselves. The US is trying to play it down. The Russians are actually criticising NK. This is very good. Russia and China both would be their most likely allies, and if we see both of them condemning these actions, that is the best we can hope for in terms of a diplomatic end to this.