I agree that is a line of thinking, with one exception. Japan is not building up its military because of N Korea but because of China. Japan's recent military

I agree that is a line of thinking, with one exception. Japan is not building up its military because of N Korea but because of China. Japan's recent military buildup didn't begin until China's really took flight. Japan always has faced little threat from N Korea (besides the nuclear weapons); NK would have to cross a significant body of water to reach Japan, and lacks the capability, and Japan has more than enough conventional power to easily defeat NK. To deal with NK, Japan needs only anti-missile and anti-air capabilities to protect against nuclear weapons. S Korea obviously is much more exposed to NK, but AFAIK their risk is not defeat to NK but losing very large numbers of civilians in Seoul, which the North holds hostage with massive, dug-in artillery batteries. That has been the North's deterrent against an SK invasion. I'm not sure if SK's military is growing.