The Rus territory of Eastern Europe stretched from Odessa on the coast to the borders of Finland in the north. The Norse in Sweden and the Slavs of the forests along the Volga River had made marriage alliances for several generations, and the rulers in Kyiv (or Kiev) typically had Norse names like Igor (Ingvar) and Oleg (Helgr). The Norse had their pantheon with Odin and Thor, the Slavs had a similar set with Dazhbog and Perun.
As Kyiv grew from a frontier trading post to have aspirations of joining the local power structure, the rulers had to consider allying by means of not only marriage but religion. Prince Igor’s widow Olga ruled for her son, and during her regency years, she was baptized a Christian in Constantinople. While her son Svyatoslav (the first Slavic ruling name) didn’t adopt her ways, one of the grandsons did. This was Vladimir, who was made prince of Novgorod and, with Swedish help, became Prince of Kyiv in 980.
Vladimir chose to ally with his grandmother’s choice, Christian Constantinople. He is said to have rejected Islam because it prohibited alcohol, and Judaism because the loss of their capital city marked them as losers in his eyes. He chose Eastern/Greek Christianity over Latin because his emissaries reported little beauty in German churches, while Hagia Sophia Cathedral impressed them greatly.
Vladimir then asked for the hand of the Emperor’s sister Anna. In 988, he was baptized a Christian (with the name Basil, like the Emperor) in the city of Kherson, Ukraine, which was originally Greek Chersonesos, then married Anna. Back in Kyiv, he tore down pagan rite centers and proclaimed the city Christian, with a new Cathedral of St. Basil. Then he sent 9000 troops to aid the Emperor in his wars.
Vladimir was not monogamous. Before Anna, he already had five wives, and after Anna’s death, he married a granddaughter of the Frankish king Otto. His marriage ties strengthened alliances and gave him a small tribe of sons to disperse into his growing kingdom.
He founded the city of Belgorod and sponsored the baptism of many of the local Turkish rulers. From his time forward, Kyiv became more Slavic and less Norse, generally more powerful, and a strong Christian force. Through his connections to Sweden, Eastern Christian missionaries went north to Norway. It’s ironic that the balance of power owed his landing on the Christian side to his love of vodka, still the controlling passion of Russia.