Principality of Chernigov
He ruled the Principality of Vladimir in Volhynia in his father's lifetime (from around 1040 to 1054). Yaroslav the Wise, who divided the Kievan Rus' among his five sons in his testament, willed the Principality of Chernigov to Sviatoslav. Sviatoslav joined his brothers, Iziaslav of Kiev and Vsevolod of Pereyaslav, in forming a princely "triumvirate" that oversaw the affairs of Kievan Rus' until 1072. The three brothers together fought against their enemies, including the nomadic Oghuz Turks, and their distant relative, Prince Vseslav of Polotsk. The Cumans defeated their united force in the autumn of 1068, but Sviatoslav routed a Cuman band plundering his principality.