Interesting. Here's a quick copy I found on Wikipedia: "A still functioning UN Command is technically the top of the chain of command of all forces in South Korea, including the US forces and the entire South Korean military – if a sudden escalation of war between North and South Korea were to occur the United States would assume control of the South Korean armed forces in all military and paramilitary moves. However, in September 2006, the Presidents of the United States and the Republic of Korea agreed that South Korea should assume the lead for its own defense. In early 2007, the U.S. Secretary of Defense and ROK Minister of National Defense determined that South Korea will assume wartime operational control of its forces on December 1, 2015. U.S. Forces Korea will transform into a new joint-warfighting command, provisionally described as Korea Command (KORCOM)."

It's worth adding that while the conflict is complicated and the lead up was long, the North was basically the aggressor in the war and that the NK army was backed 5:1 by Soviet troops.