During the rule of Boris I (r. 852–889), Bulgaria underwent major changes – the Christianization of the country and the admission of the disciples of Saints Cyril and Methodius, which marked the beginning of the creation and consolidation of the medieval Bulgarian literature and alphabet.

[2][3] The Council sealed Boris I's ambitions for cultural and religious independence[4] and calmed down the concerns among the nobility, who feared any strong Byzantine influence in the internal affairs of Bulgaria.

[6] These events ruined the Byzantine hopes to exert influence over the newly Christianized country, and Emperor Leo VI (r. 886–912) soon had a chance to retaliate.

[8][9] The ousting of the merchants from Constantinople, which was a major destination of trade routes from all over Europe and Asia, was a heavy blow for Bulgarian economic interests.

[7] The Byzantines hastily assembled a large army under the generals Prokopios Krenites and Kourtikios, which included the Imperial Guard that consisted of Khazar mercenaries.

[16] The Magyars looted and pillaged unopposed, reaching the outskirts of the capital Preslav, and after they sold the captives to the Byzantines they retreated to the north of the Danube.

[21] When Simeon I returned to Preslav "proud of the victory",[22] he broke the negotiations with Choirosphaktes and once again invaded Byzantine Thrace, further encouraged by the death of the capable general Nikephoros Phokas.

A Byzantine historian wrote:[22] ...the Romans were decisively defeated all down the line and they all perished.Among the casualties was the protovestiarios Theodosius, the second-in-command of the army, while Leo Katakalon managed to escape with a few other survivors.

According to the Muslim historian al-Tabari, Leo VI was desperate after the consecutive refusals of peace, and was forced to gather an army of Arab prisoners of war and send them against the Bulgarians with the promise of freedom.

[24] The war ended with a peace treaty which formally lasted until around Leo VI's death in 912, and under which Byzantium was obliged to pay Bulgaria an annual tribute[25] in exchange for the return of allegedly 120,000 captured Byzantine soldiers and civilians.