What factors influenced Vladimir I to choose Orthodox Christianity as the official religion of Kievan Russia?
There were likely a number of factors as to why Vladimir I adopted Orthodox Christianity. First of all, joining the Eastern Orthodox Church was a politically savvy move. His strongest neighbor, the Byzantines, functioned as the keepers of this religion. By making their church his own, he found more favor with the Byzantine rulers. This also allowed Vladimir to marry Anna, the sister of Byzantine Emperor Basil II. This marriage helped form an important alliance between the two kingdoms. It would have been highly improper for a Christian member of the Byzantine royal family to marry a pagan.
There are a number of stories surrounding Vladimir's conversation that may be apocryphal but also may have some grounding in the truth. It is said that he was considering which major religion of his neighbors to make his state religion and sent emissaries out to gather information for him. Islam was rejected because Vladimir did not like their prohibition against pork and alcohol. He considered the destruction of the Jewish Temple to be a sign that the Jews were forsaken by God. He did not like the way that Catholic kings were beholden to the Pope. It was the grandeur of the Eastern Orthodox Church that impressed Vladimir the most.
Religious matters aside, by joining the Eastern Orthodox Church, Vladimir was able to strengthen his kingdom's position. The Byzantine Empire was a strong ally commercially, economically, militarily, and politically. By making his official state religion the same as theirs, Vladimir was able to more closely strengthen his relationship with this powerful and influential neighbor.
Vladimir I wanted one religion to unite Russia. Kiev already had close economic ties with Byzantium, so it made further sense to maintain these ties with religion as well. Vladimir also did not want to be under the power of the Vatican as much of Western Europe was at the time.
Vladimir was also swayed by the iconography and the grandeur of the Eastern Orthodox Church's presence in Constantinople. The Hagia Sophia impressed him the most. Vladimir also married the sister of then–Byzantine Emperor Basil I. After Vladimir's conversion, he founded many churches for the Rus, and he was known for his charity.
Stories also exist that while Vladimir was looking for a faith to adopt, he sent underlings to research various faiths. He did not want to convert to Islam, due to the dietary restrictions. He did not want to be Jewish, due to the turmoil in Jewish history. He also did not want to be subservient to the Pope. By process of elimination, he settled on Orthodoxy. This story cannot be entirely verified historically, but it has lasted in the tradition of the Orthodox Church for generations.
Scholars believe that the main reasons for Vladimir's choice were not really religious. Instead, his reasons are said to be related to economics and power. There were reasons that pushed Vladimir towards the Orthodox Church and reasons that pushed him away from Roman Catholicism.
Kievan Rus had a lot of contact with the Byzantine Empire. They traded with one another and were in relatively close geographical proximity. Because of this, it made sense to Vladimir to maintain close ties with Constantinople. For this purpose, he wanted to marry the sister of the Byzantine emperor. He would only be allowed to do this if he converted to Orthodoxy. Vladimir did so as a way of tying his kingdom closer to the Byzantines.
The other factor was Vladimir's desire to remain free of Roman dominance. He feared that the Roman Catholic Church would try to have too much influence over what happened in Rus. Because of this, he was also pushed away from Rome (in addition to being pulled towards Orthodoxy).
Vladimir's embrace of Orthodox Christianity was largely motivated by political considerations. Previously, Vladimir had been an unabashed pagan, building a number of temples to the ancient gods. But as Grand Prince of Kyiv, he had to be pragmatic; he had to unite his fractious subjects, and Orthodox Christianity was his chosen method.
Legend has it that Vladimir chose Orthodoxy to unite his people after being impressed by tales of the dazzling worship his ambassadors had witnessed in the Hagia Sophia, the magnificent cathedral in Constantinople. But Vladimir was arguably more impressed by the immense wealth and power of the Byzantine Empire, by far and away the richest and most civilized of Kyivan Rus's neighbors. If Orthodoxy was good enough for the Byzantines, he figured, then it was good enough for him and for his subjects. By embracing Orthodoxy, Vladimir was also given the opportunity to marry into the Byzantine royal family, which he did just a year after being baptized.