South Ossetia was never a part of Georgia. It became in 1921 and after the Soviet Union stopped to exist it was declared an independent country. But apparently Georgia was not ok with that. This conflict lasts from early 90's, and always Russia was acted as a peacemaker in this conflict (there are a lot of Russians living in Ossetia). You can read about it on Wikipedia.
It's a fact that Geogria attacked Ossetia, Ossetia fighted back, then Georgia asked Russia for a help in resolving this conflict and then when Russian peacemakers reached Ossetian border, Georgia attacked them and told, that Russia started first. The US helped Georgia to spread this wrong information. This was OBVIOUSLY very well planned by Georgia, and of course the US government, who has a great interest in Georgia (basically, it's trying to surround Russia by NATO-countries to have a control of Russia). The thing that scares me most is how US government tells the people an OBVIOUS lie, and people just buy this sh*t so easily. That's unbelievable and really scary. Last place this happened was Nazy Germany.
PS: oh, and also that was Georgia who has been killing peace inhabitants and destroying Ossetians, and was even accused in genocide. And these bustards are still telling that they fight for freedom, and Russia is somehow preventing them from being a free country. That's so not true! Freedom of Georgia has nothing to deal with that, that's Ossetia who is a victim.