Supposedly the US states had an agreement not to break up the Union. South Ossetia had no such understanding with Georgia. And the Confederate states had far more in common with the Northern states than South Ossetia has with Georgia. To start with, North and South in the US Civil War at least spoke the same language. Not so in the other case.

By the way, I believe a parallel can be drawn elsewhere: specifically between "Kurdistan" and Iraq as between South Ossetia and Georgia. The only reason "Kurdistan" does not declare independence is the Kurds know the neighbors would never accept it, for fear of the reaction of their own Kurds--but they have no intention of being part of "Iraq". What are your views on this?