North Korea's land is largely unexploited. They have large untapped reserves of oil, industrial metals, etc. They could probably be very prosperous if they had a working, global economy. Though I've heard some speculate that one of the reasons the US has been so consistently hostile to North Korea (eg. violating the terms of the nuclear agreement from a few decades ago; though not to say that NK isn't an insane, dictatorial regime) is that they want to either have significant control over these resources, or they want nobody to have these resources.
That's correct. The USA is always looking for money and resources abroad and trying to manipulate public opinion to show its actions as justified. If we look at the facts, the US invaded Iraq because they were supposed to be producing nuclear weapons, which turned out to be a lie. They did not leave the country when this lie came to life, no, they kept robbing and exploiting it for years. This was the real reason for the invasion, but since the propaganda turned most of the world into its allies in this attack, there was no pressure on the USA to leave in disgrace.
The same plan is being put into motion now with NK. Show them as oppressed people in need of freedom and help from the West. Isn't that how the Vietnamese were portrayed prior to the invasion?