AFP

GEORGIAN soldiers, tanks and fighter-planes struck Tskhinvali, the capital of the breakaway (Russian-backed) region of South Ossetia, on Friday August 8th. Parts of the city were reported to be burning as Georgia's president, Mikheil Saakashvili, declared that his forces had “freed” much of the area from separatist control.

The immediate cause of the fighting is unclear as claim and counterclaim abound. But what is clear is that a conflict which has been simmering for years, has at last erupted. What happens next will depend almost entirely on Russia's response: 150 Russian tanks were reported to be entering South Ossetia on Friday. Georgia's government says that Russian planes have dropped bombs outside of South Ossetia including on the edge of Tblisi, the Georgian capital. Alexander Lomaia, the secretary of Georgia's National Security Council, told The Economist on Friday that “this is an open military aggression and we are now at the state of undeclared war with Russia. What else could you call it?”. He also said that Georgia had announced a ceasefire in South Ossetia from 3pm on Friday.

On its own, South Ossetia is unlikely to last long. It is a tiny territory run by Russia's security forces and a small and nasty clique of local thugs who live off smuggling goods and pocketing Russian aid money. According to a Georgian television channel, some 70% of Tskhinvali had been taken by government forces by the end of Friday morning.

It appears that Russia will get heavily involved—Russia's president, Dmitry Medvedev, says that he must protect Russian citizens there. The conflict could now quickly spiral into a war between Russian and Georgia, and engulf Abkhazia, a separatist region on the Black Sea coast in which Russia has much more strategic interest.

Russia says that Georgia fired first in South Ossetia and that several of its “peacekeepers” inside the territory have been killed. Last month Russia sent warplanes into Georgian airspace—to deter an attack, it said.

The row has given Russia a chance to step up pressure on Georgia, portrayed in the Russian media as a tiresome and aggressive Western stooge. The South Ossetian leader, Eduard Kokoity, said that he would force Georgian troops out of his self-declared republic (which is a patchwork of villages and small towns, some controlled by Georgian authorities and others by separatists).

The quarrel in South Ossetia follows an escalation of tension in Abkhazia. Russia has reinforced its military presence there, which is nominally part of a UN-monitored peacekeeping effort. In the past few months European governments got more involved in the peace process and Germany drafted a plan for the economic revival of Abkhazia, indefinite autonomy and the return of Georgian refugees. So far the plan has stalled. The Abkhaz authorities are uneasy about the Russian embrace, but fear the return of Georgian refugees, once the largest ethnic group in the region. Russia does not want to surrender its key role in Abkhazia.

As Russian gets involved in the war with Georgia, the disposition of political forces within the Kremlin itself may shift. Russia's prime minister Vladimir Putin, who is in China, indicated that Russia would retaliate against Georgia's aggression. Mr Medvedev may not be best pleased to start his presidency with a war in Georgia: it suggests that he may have to submit to the wishes of the hard-line military and security services. But Mr Putin has a fierce dislike of Mr Saakashvili, Georgia's maverick president, and seems determined to replace his government.

Mr Putin may also want to deal with Georgia in good time before Russia hosts 2014 winter Olympic games in Sochi, a Black-sea resort town only few miles from the Abkhaz border. A military conflict in Georgia will also derail for a long time Georgia's aspiration to join NATO—something that Russian finds deeply unpalatable.

Russia's broader aim may be to try to roll back the advance of pro-Western forces in its “near abroad” by highlighting the West's inability to help Georgia. The hotting up of Georgia's conflicts coincided with Kosovo's declaration of independence, recognised by much of the West, and American pressure for the expansion of NATO to Georgia and Ukraine. That move has been stymied, mainly by Germany; Georgia was promised eventual NATO membership but no firm plan. Though Georgia has become a vital corridor for oil and gas exports to Europe, this has not brought the support that its leaders had expected. A lame-duck American administration has been able to do little, though Georgians hope a presidential-election victory by John McCain, an ardent supporter, may change their fortunes. The country's strong-willed and idiosyncratic president, Mr Saakashvili, is not seen by all European leaders as quite the paragon of legality, freedom and reform that he claims to be. Georgia's image was severely dented in November last year by a crackdown against the opposition.