Why did Boris I convert Bulgaria to Christianity in 864?

Boris I converted Bulgaria to Christianity in 864 primarily to unify his diverse state and strengthen his central authority. By the 9th century, Bulgaria was a large, multi-ethnic realm inhabited by both Slavic majorities and Turkic-origin Bulgars. The introduction of a common, compulsory religion was a critical step in merging these groups into a single, cohesive Bulgarian ethnic community.12

Politically, the conversion allowed Boris to adopt Byzantine concepts of kingship, styling himself a ruler "by the grace of God." This provided a religious justification to suppress pagan boyars who resisted his centralized social and political order. Furthermore, adopting Christianity helped Bulgaria join the "family of Christian states," enhancing its standing in Europe.12

While Boris initially considered Roman Christianity, an unsuccessful war with the Byzantines ultimately compelled him to adopt the Orthodox faith of Constantinople in 864. This decision was part of a broader diplomatic strategy; Boris skillfully navigated the rivalry between Rome and Constantinople to eventually secure an independent Bulgarian archbishopric, ensuring the church served his nation's interests.213