what if the the North Korean regime fell and the Koreas reunified but as part of the deal US troops left? All this happened by 1993. The rest of the world was the same up to that point. Has China bullied, subordinated or otherwise made Korea its “bitch” by 2019?
To be honest, the best model for foreign policy in that case is probably the most unlikely candidate within the region, and that happens to be Mongolia. Mongolia had long been a battleground for competing influence between Russia and China, including time as part of China and as a satellite state of the Soviet Union. After Mongolia transitioned away from Communism, they wanted to be neutral/equidistant from both countries, and designed its political system and foreign policy precisely to achieve that aim. Korea could be similar in that respect, though complicated by reunification costs and all that. In that case, Korea would be neutral with respect to Russia, China, the US, and Japan. The simplest method for reunification could involve some form of federalism or decentralization à la Japan or Colombia (which would be a difference from the Mongolian model), with (most of) the former North Korean and South Korean administrative divisions coexisting side by side and the DMZ as a national peace park. China would have its role, but with Korea equidistant from all powers that would try to dominate it China wouldn't attempt to subordinate/bully/etc. a unified Korea as it hasn't dared with Mongolia. Russia, too, would want a port area for those times when Vladivostok would be unavailable (the Soviet Union worked out an arrangement with North Korea for this via Rajin, now the Rason special city), and the oligarchs would definitely want a Cyprus-like entity to park their cash just in case. The US would keep an eye via Japan; at the same time, though, although US troops would leave that would exclude the rest of
United Nations Command, so some US presence would remain as part of UNC, which could be reorganized as a temporary peacekeeping force and could help enforce neutrality (another difference from the Mongolian model).