To America of missiles North Korea will not reach, and if before the war the us military will be out in the ocean then Kim will make no sense to bomb the territory of South Korea. The same applies to Japan. Kim has no chance in this war.
North Korea is making rapid progress with their missiles. The latest test was of particular interest to the defense analysis. Some say that North Korea already possess missiles which can reach mainland US.
And even if they don't have a chance if you compare with the us military might, the fact that Kim can start a third world war would be enough reason for worry. It's not going to be about who's going to win or who's going to lose in a third world war. Once it starts, we're all going to be affected one way or another and that's nothing of the positive kind