I think you over simplify a full scale invasion and the issues that it brings. A) It gives NK justification in using any and all means necessary to defend themselves and parts of the int'l world will agree with them. Right now NK has been saying STAY AWAY from us or we will hit back. They might be insane but they know that if they launch any attacks on SK, Japan, US, AU or anyone that not even China will be able to stop the complete and total devastation of their country. Worse yet it is very, very unlikely that China (and probably Russia) wouldn't defend NK against an unprovoked (from their POV) attack on NK. This isn't Iraq where there wasn't anyone to back Hussein. If the US initiates the offensive then there will be hell to pay all over the world from it.