1) NK is China's backyard. We can't do anything without potentially involving several billion pissy Chinese.
2) Japan, Russia and China have a lot of history and thus diplomatic leverage with the kooky NK's.
3) SK is our ally. NK has a lot of artillery and troops pointed directly at the SK capital not too far from the DMZ. The capital city would likely be heavily damaged, if not destroyed if we commenced hostilites.
4) NK is starving as a result of its isolation. They won't last much longer.
|