I think a fully suported South Korea could survive without our troops there, like Japan I would want ports and airstrips to use, the Nork's best ally is China so they can't fart without clearing it with Beijing first, and China (unless she were really nuts) would not act against South Korea without incurring a lot of hurt. I think the ChiCom's have the idea that South Korea and Japan could be made moot, once they complete their "string of pearls" I think they feel they'll be in a better military and economic position with the US. The primary thrust of this new cold war is ecnomic, their military moves cannot hide their intent. They intend to be the biggest fish in the pacific basin and plan on extending their political and economic influence as far and as wide as they can, and pressuring the west (especially the US) every step of the way in their march toward global dominance. The ChiCom's are thinking and acting long term, while the rest of the world is caught up in minute-to-minute brush fires.