I think it’s more about maintaining the status quo. Their internal propaganda follows the 1984 “perpetual war” model, right down to the loudspeakers on every street corner. They need the populace to believe that they’re struggling bravely against the whole world to make them accept the conditions that they’re living in, and to justify shutting them off from the outside world. People risk torture and execution to smuggle in DVDs full of what we’d consider crappy home-improvement shows, labelled contraband propaganda by the NK state because it shows a standard of living beyond belief for the average citizen.
Externally (and @renke got there just before me), a nuclear threat is about the only thing they have to bring to the table. So they talk about crushing their puny enemies underfoot but that’s for the benefit of their own populace. Really I think the ruling class, and especially the Kim family, are just trying to hold on to what they’ve got.