You seem to forget that there are many thousands of NK refugees living outside NK, including people who escaped from gulags. I have not said categorically that the crime rate is high in NK, but there is no reason to believe it is low, and there is ample anecdotal evidence (mainly from refugees) of the kinds of crime I mentioned.
Also, you are a conspiracy theorist. First of all, there is no reason to think that the US wants to get involved in a war in North Korea. It is far too risky. Since the disaster Iraq, they have been very reluctant to get involved in any military interventions except in a very limited way. The North Korean situation is exceptionally dangerous, because they don't know what China would do. If China were to take North Korea's side out of historical loyalty, the US could find itself in the middle of WWIII. That would of course be disastrous for everyone, including the US. Second, all the sabre rattling is coming from North Korea, and none at all from the US, or even from South Korea. It would be ridiculous to say that Kim Jong-un is acting on the order of the USA. Therefore, the USA is obviously not responsible for the sabre-rattling.
What we are seeing in North Korea at the moment is nothing new at all. North Korea has been behaving like this, intermittently, for decades. Every now and then, they make threats of war, or start a small skirmish. The purpose is partly internal propaganda, designed to keep the people feeling besieged and grateful for the protection of the regime, partly as tactic to blackmail the US and other aid donors to give it more money, and partly so that the leader can convince the military generals that he's tough enough to deserve their loyalty.
The theory that the US needs to start a war there in order to sell weapons there is silly, because the region already buys plenty of weapons from the US. If you look at the data on South Korea's military arsenal, it already has enough ships, tanks, planes and missiles to bury quickly North Korea in a heap of rubble, and the majority of that equipment is from the USA.