So, a lot of people think a war against North Korea would be easy. The US military already tried that in the 50s, remember how that turned out? Oh, and back then North Korea didn't have any nukes and they were supported by China, which was a piss-poor country back then. Now imagine a war against an enemy with nuclear weapons and a country with 15 % of the world GDP on their back. Because at the end of the day, I am completely certain that China would support North Korea rather than the US. They wouldn't step in officially, because that would lead to world war 3 with a high probability to wipe out the human race, but they will support North Korea again with weapons, resources and stuff. They don't want the US to take the whole korean peninsula, they made that very clear numerous times in the past.
That's why a war is very unlikely. North Korea is just trash-talking, they won't actually launch a nuke at the US or something. They are trolling them. Sadly Trump is falling for it. I also don't see the US making the first move. Even if Trump is a moron of epic proportions, there are bound to be people on the white house stopping them from making such a stupid move.