The Golden Age of Kievan Rus' began with the reign of Vladimir the Great (980–1015), who turned Rus' toward Byzantine Christianity. During the reign of his son, Yaroslav the Wise (1019–1054), Kievan Rus' reached the zenith of its cultural development and military power. The state soon fragmented as the relative importance of regional powers rose again. After a final resurgence under the rule of Vladimir II Monomakh (1113–1125) and his son Mstislav (1125–1132), Kievan Rus' finally disintegrated into separate principalities following Mstislav's death.