Fairly obviously, it isn't in North Korea's practical interests to go to war with the USA. Without the backing of either Russia or China (or both), it would be an unwinnable conflict, and neither of those countries' governments has been holding prominent 'death to the west' rallies of late. I'm not an expert political commentator or a spook so my opinion can only be that, opinion, but I don't think I go too far in asserting that.
But more to the point, it isn't in their ideological interests to start an all-out war either. As I understand it, Americans are rather unpopular in North Korea, to put it very mildly. They hold the position of "Yankee pigs" and "sworn enemies" (Jae Young Kim gives a nice insight into the mindset here). The portrayal of the USA in North Korea seems to be somewhat equivalent to the 'Great Satan' picture that Iran pumped out under the first Ayatollah Khomeini. If this kind of propaganda output is useful to the North Korean government - say, if they wanted to unite and maintain support for their new leader, perhaps at some sort of recent mass rally in Pyongyang - then it would be in their interest to keep to the status quo.
In Nineteen-Eighty Four the three global superpowers - Oceania, Eurasia and Eastasia - supposedly exist in a state of constant warfare with no nation ever gaining the upper hand. Winston Smith, the novel's protagonist, discovers through a book supposedly written by a resistance leader that "The war is raged by each ruling group against its own subjects" - that the real object of the war is to consume the resources produced by the population without raising their standard of living, and "to preserve the special mental atmosphere that a hierarchical society needs". In other words that the war is engineered to be continuous because it is so useful to the ruling party.
It is important to note that in Orwell's world, all the warring nations are as morally reprehensible as each other in keeping the war going to oppress their populations. Unless you're Michael Moore (who expressed such a sentiment in his 2004 film Fahrenheit 9/11) it seems clear that the USA isn't interested in keeping wars going with that particular aim in mind.
But it would suit North Korea down to the ground to have a constant enemy, a perpetual scapegoat and a creeping threat to keep the people loyal and afraid - à la Orwell. And it would be very useful to show a new leader posturing loudly against that enemy, promising to settle the score and keep the people safe. If they ever managed to actually defeat the USA in any kind of conflict they would lose the opportunity to have it as a geopolitical bogeyman, and in so doing lose a method of control over their population.
This isn't to say that Kim Jong-un isn't mad or bad enough to have a crack at the USA's stealth bombers the next time they fly exercises over the Korean peninsula. I don't claim the power to predict what North Korea's foreign policies will be this time next year, or even next month. But it would be a very unwise move to take the US on: however much Kim Jong-un might hate America, right now he needs it.
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