RussiaA republic occupying much of eastern Europe and northern Asia, bounded to the north by the Arctic Ocean; to the west by Norway, Finland, Estonia, Latvia, Belarus, the Ukraine and the Black Sea; to the south by Georgia, Azerbaijan, the Caspian Sea, Kazakhstan, China, Mongolia and North Korea; and to the east by the Sea of Okhotsk and the Bering Sea. Russia has been settled by many ethnic groups, initially the nomadic Slavs, Turks and Bulgars (3–7c AD). The Byzantine Christian Church had been established by the end of the 10c. Moscow was established as a centre of political power in the north during the 14c. The overlordship of the Mongol Golden Horde was challenged successfully from 1380. Ivan III, the Great proclaimed himself ‘Sovereign of all Russia’ in 1480, and Ivan IV, the Terrible doubled the size of the empire between 1533 and his death in 1584. Internal disorder amongst a feudal nobility and constant warfare with border countries (eg Poland and Sweden) retarded Russian development until Tsar Peter I, the Great. Under Catherine II, the Great Russia became a great power, extending its territory into southern and eastern Asia. Defeat in the Russo-Japanese War (1904–5) precipitated a revolution which, although unsuccessful, brought Russia's first constitution and parliament. The Russian Revolution in 1917 ended the monarchy, and within the communist Union of Soviet Socialist Republics (formed in 1920), Russia was the dominant political force, covering 75 per cent of the Soviet area with 50 per cent of its population. With the disbandment of the Union in 1991, Russia became an independent republic and assumed the Soviet Union's permanent seat on the UN Security Council. It also became a founding member of the CIS (Commonwealth of Independent States). Relations with some former Soviet republics deteriorated in the early 1990s, and the process of transition to a market economy caused a severe economic crisis in 1993, followed by a national referendum to endorse President Boris Yeltsin's economic reforms, and increased presidential powers. In 1994 ethnic unrest in Chechnya, where Muslim Chechens declared an independent republic, resulted in the Chechen Wars. Despite failing health during the 1990s, Yeltsin clung on to power until Dec 1999, when he resigned and Vladimir Putin became President after elections in Mar 2000. President Putin was re-elected in 2004 and has asserted an increasing degree of centralization. Through the NATO–Russia Council, established in 2002, Russia participates in global discussions about security threats.