@melchizedek
the fact that Russians were a unspoken part of the conflict may have to do with pulling out. US/UN didn't want have war with Russia.
As for not wanting to unite with the North, I think thats legit concern(after seeing what happen with Germany). More likely, they would want to bring up the North's economy before uniting. Though, there are some who think North's human right abuses are lies and think it must be better because its has a communist government...