Since Korea is inextricably linked with Taiwan, China would lose tremendous face if Korean unification was dictated on American terms, as you have another situation like British victory over the Falkland islands, with Margaret Thatcher riding on the high of British victory snidingly touted perhaps the British can keep Hong Kong island from China. The same would be for the Americans, as the U.S. navy would redouble their protection of Taiwan island from China if post-unified Korea is within America's political orbit.