The history of Russia begins with that of the Eastern Slavs and the Finno-Ugric peoples. The state of Garðaríki ("the realm of towns"), which was centered in Novgorod  and included the entire areas inhabited by Ilmen Slavs, Veps, and Votes, was established by the Varangian chieftain Rurik in 862 (the traditional beginning of Russian history).  Kievan Rus', the first united East Slavic state, was founded by Rurik's successor Oleg of Novgorod in 882. The state adopted Christianity from the Byzantine Empire in 988, beginning the synthesis of Byzantine and Slavic cultures that defined Russian culture for the next millennium. Kievan Rus' ultimately disintegrated as a state because of the Mongol invasion of Rus' in 1237–1240 and the death of about half the population of Rus'. During that time, a number of regional magnates, in particular Novgorod and Pskov, fought to inherit the cultural and political legacy of Kievan Rus'.