The Christianization of Bulgaria was the process of converting 9th-century medieval Bulgaria to Christianity. When Khan Boris began his reign in 852, the international situation was very complicated. The conflict with the Byzantine Empire for the rulership over the Slavic tribes in modern-day Macedonia and Thrace was still far from being resolved. In the middle Danube region, Bulgaria's interests crossed with those of the newly created kingdom of the East Franks and the principality of Great Moravia. It was about that period when Croatia emerged on the international scene, carrying its own ambitions and demands for territories in the region. On a more global scale, the tensions between Constantinople and Rome were tightening. Both centres were competing for the Christianization that woul