After the death of Vladimir in 1015, his elder son Svyatopolk attempted to kill his brothers to become the only ruler. He managed to kill three brothers out of five, Boris, Gleb and Svyatoslav. Two of them, Boris and Gleb were unaware of the plot and did not even try to oppose the elder brother. Their moral stand turned them into martyrs and since then St. Boris and St. Gleb became the patrons of brotherly love. Svyatopolk became known as Svyatopolk Okayanny (roughly translated as Damned).
The fourth brother, Yaroslav, who was in Novgorod at the time, led the mixed army of Novgorod and Varangians to Kiev. In spite of assistance given to Svyatopolk by the Polish king Boleslav the Brave, Yaroslav drove away Svyatopolk, who later died somewhere in exile. The last brother, Mstislav, lived in the southern city of Tmutorokan. For some reasons, a war started between Yaroslav and Mstislav, and the country was split between them. Yaroslav ruled Kiev and the lands to the West from Dnieper, while Mstislav was the ruler in Chernigov and the lands to the East from Dnieper. Only after Mstislav died, Yaroslav succeeded in re-uniting the Russian lands (1034).
Yaroslav became known as Yaroslav the Wise. He collected a large library of Russian and translated Greek books in the temple of St. Sophia in Kiev, and the library was available to the public audience. By his orders, many schools and churches were built all over Russia.
He was also a successful military leader. So, he defeated Pechenegs and freed Kiev from their incessant raids (1034). The majority of Pechenegs left to the Balkan peninsula and those who stayed, pledged loyalty to Russian knyazes and settled along river Ros (a right tributary of Dnieper). They were known as 'karakalpaks' (black hoods) since then. Yaroslav undertook an unsuccessful raid to the Byzantine empire, but the ensuing three-year long war ended by liberation of Russians prisoners taken during the raid.
The state was rich enough to afford large and rich edifices. So, Yaroslav built outstanding temples of St. Sophia in Kiev and Novgorod. He invited Greek architects to build these churches. Yaroslav sent his ambassadors and merchants to Germany, France, Hungary, Poland and Scandinavia. Many foreign rulers became his relatives. Yaroslav himself was married on a Swedish princess Ingigerd (Irina in Russian), three hes sons married daughters of German kings, his daughters married French, Hungarian and Norse kings, and his fourth son, Vsevolod, married a woman from Constantinople who was a relative of emperor Constantine Monomakh. So, under Yaroslav, Russia became a full-fledged European country and Kiev became an important European trade centre, shaping the trade between European markets and the Orient.