In the early ninth century two pre-state unions with the centers in Kiev and Novgorod were established. They united both East Slavic tribal groups - the northern and the southern.
Rurik, the Prince of Novgorod, died in 879; and three years later Oleg, who was appointed a custodian of Rurik’s son and heir, Igor, united Kievan and Novgorod states. Thus, a united ancient Russian State, Kievan Rus, with Kiev as center, was established. It happened in 882.
Kievan Rus became one of the major European medieval states in the 9th – 11th centuries.