Matt McCarten this morning suggests the following reason for Russia's intervention into Georgia
the Georgian military assault killed dozens of Russian peacekeepers and hundreds of civilians before Russia stepped in.
This is what an eye witness says really happened
What happened here is the South Ossetia militia (instructed by Russia) started firing on Georgian villages outside of South Ossetia. The Russian "peacekeepers" then said they had lost control of the militia (strangely not sending re-inforcements at this time). Georgian's did not return fire for a long time until severe civilian casualties were recorded on the Georgian side in the villages. Georgia then decided to take action, which is what the Russians had ensnared them into, then they justified a complete pre-planned invasion of Georgia.