Our military policy in Korea since the war ended has been to leave a large force of troops there at the DMV as a "tripwire." In other words, they are a guarantee we will not stay out if the North Koreans attack again because they are essentially acting as hostages.
Bush suggested a few years back that they should be repositioned, so they would be less at risk if a new hot war started there over N. Korea's nukes. I haven't heard a thing since about whether the plan has been implemented.
But one thing is for sure. We can't afford to leave our troops exposed like that if the South Koreans don't intend to remain our allies. They are far too vulnerable, especially if they remain at the DMV.
DMZ.