Following the defeat of the Byzantine army in the initial stages of the war in 894 Leo VI sought aid from the Magyars who at the time inhabited the steppes to the north-east of Bulgaria.

With the Magyar threat eliminated, Simeon led his hosts south and routed the Byzantine army in the battle of Boulgarophygon in the summer of 896, which forced Byzantium to agree to the Bulgarian terms.

During the reign 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.

[6][8] In 894 Stylianos Zaoutzes, basileopator and leading minister of Leo VI the Wise (r. 886–912), convinced the emperor to move the Bulgarian market from Constantinople to Thessalonica.

[9] That move affected not only private interests but also the international commercial importance of Bulgaria and the principle of Byzantine–Bulgarian trade, regulated with the Treaty of 716 and later agreements on the most favoured nation basis.

[10] The Byzantine chronicler Theophanes Continuatus described the reasons for the conflict as follows: The cause of the war was the following — the basileopator Stylianos Zaoutzes had a eunuch slave named Mousikos.

[8][9] However, many historians including Vasil Zlatarski and John Fine consider those claims unlikely, arguing that in the beginning of his reign Simeon needed to consolidate his power and imperial ambitions had not yet been crystallised, therefore his military intervention was a defensive act to protect the Bulgarian commercial interests.

[10][15] In the autumn of 894 Simeon I launched an invasion of Byzantine Thrace, taking advantage of Byzantium's engagements with the Arabs to the east, which had left the Balkan provinces vulnerable.

Leo VI hastily assembled an army under the generals Prokopios Krenites and Kourtikios and many archons, which included the Imperial Guard that consisted of Khazar mercenaries.

[24] While Simeon concentrated his forces along the southern border to confront Phokas, the Byzantine navy under admiral Eustathios Argyros sailed to the Danube Delta to assist the Magyars.

[26][28] Facing a difficult situation with war on two fronts, Simeon sent a peace proposal through admiral Eustathios to buy time to deal with the Magyar menace, promising to return the Byzantine captives.

Instead, Simeon I exchanged letters with him, protracting the negotiations, showing suspicions over the wording of the Byzantine proposals, constantly seeking clarifications and adding new demands.

[34] The blow on the Magyars was so heavy that they were forced to migrate further west in search of new pastures, eventually settling in the Pannonian Basin, where they established the powerful Kingdom of Hungary.

Leo VI, who was in a difficult situation, facing the Arabs in the east and deprived of the services of the capable general Nikephoros Phokas, who was either disgraced as a result of the intrigues of Stylianos Zaoutzes or died in early 896, had to comply.

[33] The Byzantine sources have not recorded the aftermath of the battle but, according to the accounts of the contemporary Arab historian Muhammad ibn Jarir al-Tabari, the Bulgarians marched towards Constantinople.

Leo VI was in such a panic that he considered arming Arab prisoners of war and sending them against the Bulgarians in return for their freedom, but eventually abandoned the idea.

[34] The war ended with a peace treaty which confirmed the Bulgarian domination on the Balkans,[39] restored the status of Bulgaria as a most favoured nation, abolished the commercial restrictions and obliged the Byzantine Empire to pay annual tribute.

[43] In addition, Simeon I took precautions to reduce the Byzantine influence over the Western Balkans by imposing his authority over the Principality of Serbia in return for recognizing Petar Gojniković as its ruler.