Russia is the largest country in the world, occupying a huge part of both Europe and Asia. According to legend, Slavic tribes of Novgorod invited the Varangian (Viking) king Oleg to bring order to their land. Oleg established the Kievan Rus' in this realm, the first Russian state. By the 11th century, the Kievan Rus' had disintegrated into lesser princedoms, which were once again united into one state by Ivan III in the 15th century. After a decisive victory over Sweden and large territorial gains, Peter I pronounced the Russian Empire in 1721. The Russian Empire lasted until 1917 when a socialist revolution dethroned the last Russian emperor. After the dissolution of the USSR in 1991 Russia appeared on the world map again, now as a federal republic.