The history of Russia begins with the histories of the East Slavs, Turkic and the Finno-Ugric peoples. The traditional start-date of specifically Russian history is the establishment of the Rus' state in the north in 862 ruled by Vikings. Staraya Ladoga and Novgorod became the first major cities of the new union of immigrants from Scandinavia with the Slavs and Finno-Ugrians. In 882 Prince Oleg of Novgorod seized Kiev, thereby uniting the northern and southern lands of the Eastern Slavs under one authority. The state adopted Christianity from the Byzantine Empire in 988, beginning the synthesis of Byzantine and Slavic cultures that defined Orthodox Slavic culture for the next millennium. Kievan Rus' ultimately disintegrated as a state due to the Mongol invasions in 1237–1240 along with the resulting deaths of about half the population of Rus'. After the 13th century, Moscow became a cultural center. The territories of the Grand Duchy of Moscow became the Tsardom of Russia in 1547. In 1721 Tsar Peter the Great renamed his state as the Russian Empire, hoping to associate it with historical and cultural achievements of ancient Rus' - in contrast to his policies oriented towards Western Europe. The state now extended from the eastern borders of the Polish-Lithuanian Commonwealth to the Pacific Ocean. Peasant revolts were common, and all were fiercely suppressed. The Emperor Alexander II abolished Russian serfdom in 1861, but the peasants fared poorly and revolutionary pressures grew. In the following decades, reform efforts such as the Stolypin reforms of 1906-1914, the constitution of 1906, and the State Duma (1906-1917) attempted to open and liberalize the economy and political system, but the Emperors refused to relinquish autocratic rule and resisted sharing their power. A combination of economic breakdown, war-weariness, and discontent with the autocratic system of government triggered revolution in Russia in 1917. The overthrow of the monarchy initially brought into office a coalition of liberals and moderate socialists, but their failed policies led to seizure of power by the communist Bolsheviks on 25 October 1917 (7 November New Style). Between 1922 and 1991 the history of Russia became essentially the history of the Soviet Union, effectively an ideologically-based state roughly conterminous with the Russian Empire before the 1918 Treaty of Brest-Litovsk. The approach to the building of socialism, however, varied over different periods in Soviet history: from the mixed economy and diverse society and culture of the 1920s through the command economy and repressions of the Joseph Stalin era to the 'era of stagnation' from the 1960s to the 1980s. From its first years, government in the Soviet Union based itself on the one-party rule of the Communists, as the Bolsheviks called themselves, beginning in March 1918. By the mid-1980s, with the weaknesses of Soviet economic and political structures becoming acute, Mikhail Gorbachev embarked on major reforms, which eventually led to the overthrow of the communist party and the breakup of the USSR, leaving Russia again on its own and marking the start of the history of post-Soviet Russia. The Russian Federation came into being in January 1992 as the legal successor to the USSR. Russia retained its nuclear arsenal but lost its superpower status. Scrapping the socialist central planning and state-ownership of property of the socialist era, new leaders, led by President Vladimir Putin (who first became President in 2000), took political and economic power after 2000 and engaged in an energetic foreign policy. Russia's 2014 annexation of the Crimean peninsula has led to economic sanctions imposed by the United States and the European Union. In 2006, 1.5-million-year-old Oldowan flint tools were discovered in the Dagestan Akusha region of the north Caucasus, demonstrating the presence of early humans in Russia from a very early time.The discovery of some of the earliest evidence for the presence of anatomically modern humans found anywhere in Europe was reported in 2007 from the deepest levels of the Kostenki archaeological site near the Don River in Russia, which has been dated to at least 40,000 years ago. Arctic Russia was reached by 40,000 years ago.That Russia was also home to some of the last surviving Neanderthals was revealed by the discovery of the partial skeleton of a Neanderthal infant in Mezmaiskaya cave in Adygea, which was carbon dated to only 29,000 years ago. In 2008, Russian archaeologists from the Institute of Archaeology and Ethnology of Novosibirsk, working at the site of Denisova Cave in the Altai Mountains of Siberia, uncovered a 40,000-year-old small bone fragment from the fifth finger of a juvenile hominin, which DNA analysis revealed to be a previously unknown species of human, which was named the Denisova hominin. During the prehistoric eras the vast steppes of Southern Russia were home to tribes of nomadic pastoralists. In classical antiquity, the Pontic Steppe was known as Scythia. Remnants of these long gone steppe cultures were discovered in the course of the 20th century in such places as Ipatovo, Sintashta, Arkaim, and Pazyryk. In the later part of the 8th century BCE, Greek merchants brought classical civilization to the trade emporiums in Tanais and Phanagoria. Gelonus was described by Herodotus as a huge (Europe's biggest) earth- and wood-fortified grad inhabited around 500 BC by Heloni and Budini. The Bosporan Kingdom was incorporated as part of the Roman province of Moesia Inferior from 63 to 68 AD, under Emperor Nero. At about the 2nd century AD Goths migrated to the Black Sea, and in the 3rd and 4th centuries AD, a semi-legendary Gothic kingdom of Oium existed in Southern Russia until it was overrun by Huns. Between the 3rd and 6th centuries AD, the Bosporan Kingdom, a Hellenistic polity which succeeded the Greek colonies, was also overwhelmed by successive waves of nomadic invasions, led by warlike tribes which would often move on to Europe, as was the case with the Huns and Turkish Avars. A Turkic people, the Khazars, ruled the lower Volga basin steppes between the Caspian and Black Seas through to the 8th century. Noted for their laws, tolerance, and cosmopolitanism, the Khazars were the main commercial link between the Baltic and the Muslim Abbasid empire centered in Baghdad. They were important allies of the Byzantine Empire, and waged a series of successful wars against the Arab Caliphates. In the 8th century, the Khazars embraced Judaism.