Now you are reaching. Any EMP effect would not be confined to the US. NK would pay a huge price including military retaliation. If they announced beforehand that it was a test, then they would be issued an ultimatum that should it go forward, they will be wiped out. If they don't announce it, then any such explosion would be considered an attack and a response would be soon in coming. Retaliation won't be left for the UN to decide.
They have kidnapped citizens of foreign powers and kept them as slaves for decades. They admit it and they are still holding these people. They have committed more acts of terror than any other regime in modern history, including blowing up airplanes with diplomats of "friendly powers," such as China, on board. They have starved over a million of their own people. They are currently holding us up because we stopped them from distributing billions of dollars in counterfeit $100 bills that they had produced. And they demand the money back from that criminal endeavor as their price for returning to negotiations over their nuclear program.
They are not rational. That's the part that so many who have argued with me today reject and really the only point on which we disagree. If you can't accept that possibility then, in my opinion, you haven't got a broad enough view of the world to imagine what might happen and therefore, in my view, you can't analyze the situation effectively. Stuff happens beyond what we consider to be reasonable and acceptable. We have to be able to think beyond what we consider reasonable and acceptable.
Will they do it? I have no idea. Might they do it? Absolutely. You (and others here) reject that possibility out of hand and I think that is a serious mistake. You have the odds on your side. But then, the odds were against the Anschluss or Pearl Harbor and certainly against 9/11 being carried out. In the case of Pearl Harbor the leading military minds of the time, including those in Japan, said it was insane. The Anschluss was the result of 30 years of humiliation and despair, coupled with a madman's twisted dream. In the case of 9/11 you had a bunch of religious fanatics who had their own reality and welcomed the consequences. What makes you think that the Iranian or North Korean or Venezuelan leaders are any more connected with reality than the NAZIs, Al Qaeda or the Imperial Japanese?
Not only is the universe stranger than you imagine, it is stranger than you can imagine.
--J. B. S. Haldane