I promise I’m going to try and avoid simply cherrypicking Henry’s posts, but I did want to add a little bit to his insightful bit on North Korea, which focuses on some of the diplomatic fallout that would ensue from a horrifically misguided attack of North Korea. As for military reasons, people tend to forget that any military action would likely be met with the destruction of Seoul, which is within artillery range of the North Korean border.
Beyond the calamitous impact this would have on South Korea, North Korea’s eventual fall would also create a simply massive humanitarian problem. North Korea is home to a distressingly malnourished and impoverished populace, and going to war without a plan for how to address this situation would make invading Iraq look a case study in responsibility.
So, to sum things succintly, military action would harm alliances, wreak havoc on the civilian population of an ally, and commit invaders to a reconstruction effort. Terrible, terrible idea.