The five days war between Georgia and Russia because of South Ossetia in August 2008, which dominated the international political and diplomatic agendas for some weeks, has raised a lot of difficult questions – factual and legal ones. Before the war only a small number of experts in Europe and beyond was well informed about South Ossetia, its history and its complicated contemporary situation within the Caucasus conflict region. Therefore the outbreak of the war was a totally surprise for the international community of states. Before discussing the legal problems of the war the article in its first part gives a short perspective upon the nearly unknown history of South Ossetia.Under Soviet rule South Ossetia had the formal status of a national autonomous administrative entity within the Socialist Republic of Soviet Georgia being integrated in the USSR. During the decline of the Soviet Union South Ossetia by relating to public international law principle of self-determination of the people declared to be a Republic, i.e. a sovereign national state. But it was internationally not recognized as a state, despite the fact, that South Ossetia fulfilled the key criteria of statehood. Instead, the bloody ethnic conflict between Ossetes and Georgians was internationalized by armistice and non-aggression agreements between Russia and Georgia (1992; 1994; 1996). Anyway, since that time South Ossetia possessed the legal status of a »stabilized de facto Régime« (J. A. Frowein), and as a consequence it was a partly international law legal entity (partielle Völkerrechtssubjektivität).The article proves the fact that Georgia's president Micheil Saakashwili had started the war by commanding an armed attack against the capital of South Ossetia, Zchinwali, and surrounding villages on 7th August 2008. Thus Georgia violated the principle of the general prohibition on use of force (art. 2, 4 UN-Charter) without being entitled to refer to the right of self-defense (art. 51 UN-Charter). Georgia during the attack as well as violated some humanitarian international public law rules provided in the Geneva Conventions.On the opposite Russia's counterattack is basically justified by the right to self-defense, but during the attack it violated the legal principles of proportionality and necessity by occupying large areas of Western Georgia, far from the South Ossetia conflict zone. Above that Russia had violated the international law principle of non-intervention into domestic affairs of Georgia and as a result it has seriously contributed to the escalation of the South Ossetian conflict up to war.