From the Ukrainian experience, the Russians became convinced that the United States was engaged in a plan of strategic encirclement and strangulation of Russia. From the Kosovo experience, they concluded that the United States and Europe were not prepared to consider Russian wishes even in fairly minor affairs. That was the breaking point. If Russian desires could not be accommodated even in a minor matter like this, then clearly Russia and the West were in conflict. For the Russians, as we said, the question was how to respond. Having declined to respond in Kosovo, the Russians decided to respond where they had all the cards: in South Ossetia.
Moscow had two motives, the lesser of which was as a tit-for-tat over Kosovo. If Kosovo could be declared independent under Western sponsorship, then South Ossetia and Abkhazia, the two breakaway regions of Georgia, could be declared independent under Russian sponsorship. Any objections from the United States and Europe would simply confirm their hypocrisy. This was important for internal Russian political reasons, but the second motive was far more important.
[…] By invading Georgia as Russia did (competently if not brilliantly), Putin re-established the credibility of the Russian army. But far more importantly, by doing this Putin revealed an open secret: While the United States is tied down in the Middle East, American guarantees have no value. This lesson is not for American consumption. It is something that, from the Russian point of view, the Ukrainians, the Balts and the Central Asians need to digest. Indeed, it is a lesson Putin wants to transmit to Poland and the Czech Republic as well. The United States wants to place ballistic missile defense installations in those countries, and the Russians want them to understand that allowing this to happen increases their risk, not their security.
[George Friedman, Stratfor, August 12, 2008: “The Russo-Georgian War and the Balance of Power”.]