How did Christianity become the state religion of Kievan Rus?

The adoption of Christianity as the state religion of Kievan Rus was a strategic and political process centered on the reign of Vladimir I.

While Christian influence had existed in the region prior to his rule—notably through the baptism of his grandmother, Saint Olga—Vladimir remained a pagan until the late 10th century. In approximately 987, the Byzantine emperor Basil II sought military assistance from Vladimir to quell internal insurrections. A pact was formed in which Vladimir agreed to provide military aid in exchange for the hand of Basil’s sister, Anne, in marriage, with the condition that Vladimir convert to Christianity.123

Following his baptism, Vladimir ordered the conversion of his people, suppressing traditional pagan practices in Kyiv and Novgorod. The state adopted the Byzantine rite, and the church was established as an ecclesiastical province subordinate to the patriarch of Constantinople. This integration facilitated the spread of Byzantine culture, art, and the Old Church Slavonic liturgy throughout the Kievan Rus state.1342