You brought up every major point I would have brought up with this issue. The one thing that you didn't mention though is that North Korea is basically a fly compared to the United States. There is no way Kim Jong-un would be dumb enough to attack Seoul, South Korea or anywhere else for that matter. The North Korean government has to be aware that if that tried anything they would be squashed completely within less than a month. They have no real allies, and while they may be a blemish on the face of humanity, they are far from the biggest threat to America.