lol I'm Korean, ya know? the word in Korea is that South Korea will fall if North Korea invades. simple - extremely massive hostile force. South Korean and Americans troops will be immediately overwhelmed and they stand no chance at all. how fast can America ships their troops to Korea? ....... if they can manage to land in Korea at all....
Korean War ain't over, ya know? over 50 years and still going.... the most challenging part about Korean War is the mountains. Koreans know their mountains well and they know how to fight in it. Americans don't. That's why they had hard time winning Korean War and Afghanistan. The Americans are pretty much helpless without their tanks and APC. oh yea - Vietnam War, remember?
Iraq is nothing comparable to Korea... Iraq is just one big flat desert country and it's easy for Americans to roll in tanks, planes, etc. Korea? Afghanistan? nope. It wasn't easy for Americans. and that's why Soviet Union gave up.
think about this - there are hundreds if not thousands of missiles pointed at Seoul. so what's the point of "obliterating" North Korea if Seoul is destroyed? beside.... North Korea can rebuild itself since it's a military regime and its HQ is extremely mobile. South Korea is extremely vulnerable and will not be able to recover its economic status for a couple decades or so. but why isn't NK invading yet? because the elite class is not interested. they rather bathe in their stolen wealth than to engage in war and get killed.
North Korea is actually supposedly controlled by dozens of elitists - many of them are generals and well-connected high-ranking government officials... not Kim Jong-Un as he is just a puppet for them to avoid public spotlight.
Like his late father, Kim Jong-Un constantly faces assassination attempts, coup d'etat, and power struggles. That's why both Kim Jong-Un and Kim Jong-Il are very paranoid, delusional, and secluded. truly a very lonely world for them.