In response to a request for some background on the current Georgia-Russia conflict, I recently posted a link to this BBC primer and the following, very-high-level explanation to Greg Rucka's blog. The explanation seemed decently concise and clear, so here it is again:
South Ossetia's majority Ossetian population do not want to be part of Georgia, and took the first opportunity to try and separate in 1991 in the nascent days of the most recent incarnation of Georgia as a nation.*
The Russian government, seeing opportunity, supported the Ossetian separatists, including sending in "peacekeeping" troops who make it tricky for Georgian forces to do anything about continued violence coming out of the region.
Last week, increasing yet still low-level exchanges of fire between Georgian and Ossetian forces led to a call for peace talks, a four-hour ceasefire, and then a full military incursion by the Georgian military into S. Ossetia. The official Georgian line is that they took this action in response to a new outbreak of attacks by Ossetian forces. This may well be true, as many analysts believe the S. Ossetian authorities have been trying to provoke a violent enough incident to get the Russians involved in a big way.
Apparently, that happened, as the Russians rolled into S. Ossetia in force, and then continued their assault with air attacks across all of Georgia. They appear to have also bisected the country with their land forces now.
There is also the possibility that Georgia's president (Saakashvili) thought he could draw the US into events if things went awry. If so, that was a miscalculation on his part.
So Russia has certainly been promoting this situation for years, most likely hoping for something exactly like this, but the current Georgian regime did itself no favors by how it has acted toward these breakaway regions.
*Clarification -- This conflict does go back significantly farther than 1991, but 1991 is when things boiled up this time around. This does seem to be the way of things in Europe, and Eastern Europe in particular.