South Ossetia lies on the southern slopes of the Caucasus, a mountain range that is home to some 50 different ethnic groups, many speaking mutually incomprehensible languages and with long histories of violent enmity.
The Caucasus were brought under Russian control in a series of wars in the 19th century, fought against not only the often fiercely-independent local peoples but the Persians and the Ottomans, who coveted the high ground between the Black and Caspian seas.
The people of the Caucasus, many of whom adhered to ancient traditions and were resentful of outsiders' attempts to control them, were perhaps the most troublesome subjects of Tsarist Russia and the Soviet Union that succeeded it. Stalin – whose father was reputed to be Ossetian – in 1922 divided control over Ossetia between the Georgian and Russian Soviet republics, a move which angered Ossetians and prompted occasional protests over subsequent decades.
When the South Ossetians attempted in 1989 to reunite with ethnic kin in Russian-controlled North Ossetia, the Georgian nationalist Zviad Gamsakhurdia marched supporters into the region to confront the secessionists.
In 1989-91, as the Kremlin's hold over its empire crumbled, the Caucasus witnessed a surge in nationalism. Regions like Chechnya declared independence from Moscow but in South Ossetia, local leaders proclaimed their region part of the Russian Federation rather than the emergent sovereign state of Georgia.
Sporadic clashes between Georgians and South Ossetians – who had mostly lived together in peace for decades, often inter-marrying – continued until 1991, when Tbilisi sent in troops to crush the separatist movement. More than 2,000 people are believed to have died in the fighting.
After a coup toppled Mr Gamsakhurdia as president, his successor, Eduard Shevardnadze, agreed a deal with Boris Yeltsin for Russian peacekeepers to monitor a ceasefire. When Mikheil Saakashvili, below, ousted Mr Shevardnadze in the 2003 Rose Revolution, he vowed to bring South Ossetia and another breakaway region, Abkhazia, back under Tbilisi's control.
He accuses Russia of sending cash and weapons to separatists in both regions, to ensure continued Kremlin influence in the oil-rich Caucasus – the BTC pipeline carrying oil from Azerbaijan to Turkey is routed through Georgia – and to undermine Georgia's bid to join Nato.
Russia has given passports to the vast majority of South Ossetians and Abkhazians, and pledges to defend its citizens in those provinces. Many South Ossetians say they expect other Caucasian peoples to support their fight against Georgia, and reports are emerging of volunteers heading for the region from Abkhazia and North Ossetia.