A guy I work with retired from the Army last June, from Camp Page. He has a theory that the unification of the peninsula could be brought about by a North Korean attack on Japan, which would be applauded and supported by the majority of people in the ROK. Hatred of the Japanese is the great unifying factor, and would make a US response against the North launched from US bases in the ROK impossible.
When I was in Korea back 20 years ago Korean antipathy for Japan was understood, but muted. Have Korean-Japanese relations deteriorated significantly in the last several years?
US Forces in Korea cannot function without Host Nation Support; I'd venture to say that most American installations have more Koreans on them than Americans. If the NKs lobbed a nuke at Tokyo and the ROKs thought that was just fine with them, 2ID could wake up one morning surrounded, disarmed and interned, and there wouldn't be a heck of a lot they could do about it. Same with the Air Bases. Kinda makes ya think about our whole West Pac/Far East strategy.
Read Proud Legions by John Antal for a damn good account of what land warfare in Korea could be like this go around. It ain't 1950 anymore. This book assumes the ROKs are on our side.
This isn't the case anymore. The Yen is pretty strong with the Won and most Korean cities cater more the the Japanese then any other people. They speak good Japanese and know the power of money. The younger generation doesn't have the distrust of the Japanese that the older generations do.