The problem was that Georgia was trying to retake the separatist province of South Ossetia. While Georgia was doing this, Russia invaded South Ossetia and started fighting the Georgians (helping the rebels), saying that Georgia was killing Russians that were in South Ossetia. All this comes at a time when Georgia is trying to join NATO (North Atlantic Treaty Organization, something Russia is against) and Russia is increasing its aggressivity towards the West.
(Please click the pictures to see them in their original size)
Oil gets into the game
Oil gets into the game
Additional Information
Russia is 244.9 times larger than Georgia.
Russia's area is 17,075,400 km² while Georgia's area is 69,700 km²
Georgia's Flag
Georgia's Map
Russia's Flag
Russia's Map
A video from YouTube explainig Georgia's oil problem