I have deliberately avoided this thread, but I will post some thoughts and then go away again.

In 1966, Kim Il Song announced and began what has since become known (among those who know of it) as the "DMZ War" or the "The Second Korean Conflict." Highlights of this include the Blue House Raid, the capture of USS Pueblo, and the shoot-down of the US EC-121 "spy plane" (oh, go look them up!). Between 1967 and the end of 1969 the DPRK attacked forces of both the Republic of Korea and the US, causing death among both the military and the civilian populations.

Kim Il Song did this "in support of his Socialist brethren" in Vietnam and elsewhere: i.e., the US was focused on Vietnam and he felt it a good time to start a "People's Uprising" in South Korea (it backfired mightily on him). I recommend reading Daniel P. Bolger's "Scenes From An Unfinished War" (Leavenworth Papers No. 19) for a good history of this period.

With the US tied up in Afghanistan, why wouldn't the same thinking apply now? In 1968-69, the US had about 56,000 troops in ROK, now the US has about 28,000 troops there. However, the ROK Army was well-equipped and trained then and is even moreso now.

Military estimates believe that the DPRK could fight a war for about 30 days on the supplies it has; the ROK could last six or more months. The US forces could hold the attack route north of Seoul and the Chorwan Valley until the ROK Army could move.

EVEN WITH NUCLEAR WEAPONS used by the DPRK, perhaps especially so, it would make no difference in the outcome. Russia is no longer the USSR and is very unlikely to get involved on either side; China would lose its trade relationship with its largest trading partner, the US, if it joined with the DPRK -- and these days China is into making money and not exporting "revolution". Should nuclear weapons be used in a Korean fight the world would be appalled and DPRK might well face the prospect of an invasion BY China and Russia from the North because of the destabilization it caused.

I think that if Kim Jong Il did order an attack on the South he would be assassinated by his senior military commanders who actually KNOW the score and do not live in a dream world of iPods and gold-plated pistols.