A friend asked why I thought Russia invaded Georgia. First of all, although we say, "Russia invaded Georgia" what we really mean is that some units of the Russian military entered Georgia's territory and destroyed things and killed people. It wasn't the whole Russian nation that did this, but some soldiers, who took orders from the government, and I don't know how representative the Russian government is of Russia as a whole. It seems to me the Russian government keeps a pretty tight control on what Russian people know about the world, and shapes domestic opinion in such a way that it's difficult to know what Russian people would really want or do if they knew what people outside of Russia know. Also, nations and governments are made up of thousands of people with thousands of different opinions and values and motives. When a country does something like send units of its military into another country, there will be various reasons for this, and some of the generals or political leaders that ordered the intervention or invasion will have quite different motives or understandings than their colleagues. But, that said, here are reasons I suppose Russians decided to send some military units into Georgia, going as far as Gori (a city I've actually visited, in 1985).
1st. The Russians must maintain credibility with their allies, and the South Ossetians are their allies, so they had to respond to the Georgian attack on South Ossetia.
2nd. The Russians desire that South Ossetia will gain its independence or perhaps join with North Ossetia as part of the Russian Federation, and so they want to stop Georgia from daring to exert control over South Ossetia.
3rd. The Russians feel a moral obligation to protect ethnic groups they perceive to be oppressed. From the Russian point of view, the South Ossetians are oppressed by the Georgians, and so they must punish the Georgians for attacking South Ossetia. (Some Russians see the South Ossetians the way some Americans see the Kosovo Albanians, the Tibetans, or the persecuted minorities in Sudan).
4th. Certain figures in the Russian government and military wanted to make a demonstration of strength to demonstrate that Russia is still a powerful country. This is mainly for domestic consumption, to keep up Russian loyalty to the elites who control Russia, but it is also a communication to nations around Russia, that they must be careful in their diplomatic and military actions, because Russia is not afraid to intervene (or invade). In essence, the invasion of Georgia was a morale booster for Russia and a way to intimidate other countries.
5th. Russian political elites wanted to stop NATO from enlarging, and wanted to show that if NATO included states too close to Russia that have unresolved diplomatic problems, this could draw NATO and Russia into military conflict. The Russian elites expect that this will make the NATO elites reconsider extending NATO membership to Ukraine and Georgia.
6th. Russian elites have a intuitive hatred of the current administration in Georgia, and were eager to attack Georgia to destabilize it and drive its current administration out of power.
I think the domestic morale booster rationale should be ranked pretty high. Also, the humans running the Russian government and military are vulnerable to the same irrational hubris and short-sightedness that plagued American elites who decided we would fight a certain sort of war in Afghanistan and Iraq. It's old world thinking.
Now for my opinion of the whole thing. It's ridiculous to fight over land. The desire of the Abkhazians and South Ossetians for independence from Georgia is not comparable to the desire of the Confederate States of America for independence. There is no ideological bond or historical reason why those little enclaves should be part of either Georgia or the Russian Federation. The fact that those people find themselves within the borders of one or the other administrative state hardly matters, and certainly isn't worth a bloody war. If Russia can get independence for South Ossetia and Abkhazia, this would set an interesting precedent for Tibet, where people would like greater independence or autonomy from China. I think northeastern Sri Lanka where the Tamils want greater autonomy or independence, Kashmir, and some of the provinces in the Democratic Republic of the Congo could all point to what happened in Kosovo and what may happen in South Ossetia and Abkhazia and ask, "why not here for us?"
Also, I wonder if Russia's government's desire to remove Georgia's Saakashvili from power is similar to the American government's desire to remove such political leaders as Manuel Noriega in Panama (1989), Saddam Hussein in Iraq (2003), Jacobo Arbenz Gusmán in Guatemala (1954), Mohammed Mosaddeq in Iran (1953), Patrice Lumumba in the Congo (1961), Dgo No Dingh Diem in South Vietnam (1963), Salvador Allende in Chile (1973), or Bernard Coard and Hudson Austin in Grenada (1983). Noriega, Hussein, Diem, and Austin were bad guys, and I'm glad someone removed them from power. But Gusmán, Allende, Mosaddeq, and Lumumba weren't so bad at all, and it's a crime that our government had a hand in stripping them of power (and in some cases, having them killed). I think Russia is behaving as the United States did in these sorts of situations, and with Saakashvili I think we have a leader who is flawed but overall pretty good (like Lumumba or Allende), not a bad guy like Austin or Hussein or Noriega. So Russia is blameworthy the way the United States was when it waged an undeclared war against Nicaragua in the 1980s. The Georgians (like the Sandanistas in Nicaragua) are not saints, and they deserve harsh criticism for some of their actions (especially the murderous attack on South Ossetians that triggered the Russian invasion), but the response by Russia, like America's foreign policy in the 1980s, is wrong.
But it's difficult to say. I don't follow Georgian or Russian politics. I have my hands full keeping track of developments in Iraq. Recently the Kurdish leader Masoud Barzani called al-Maliki's government "totalitarian" and I'm worried about what the Peshmerga might do in Kirkuk. And did anyone notice that very few (hardly any) of the Awakening Council tribal leaders attended the handover of al-Anbar in Ramadi? I think the Iraqi Islamic Party was behind the (temporary) ouster of al-Anbar police chief Major General Tareq Youssef al A'sal al Dulaimi. I think this means the Iraqi Accord Front is going to try to rig the 2009 elections where they can, and that could be disastrous.