Bulgaria emerged and received official recognition following two victories over the cosmopolitan Byzantine empire. The first battles took place in the Danube delta area in the year 680 A.D. The conflicts continued in the following year, spreading south of the Balkan Range. This is cited in the Acts of the Sixth Oecumenical Council of the Christian Church in Constantinople (present-day Istanbul). This council, over the course of almost a year, debated and asserted - in opposition to the monothelitic heresy - the official thesis that Christ had two wills, one divine and the other human.

On March 18th, 681, the Byzantine emperor Constantine IV Pagonatus departed from the Council to curb the incursions of the Proto-Bulgarians into Thrace, which violated the wholeness of the empire. But he failed to break their dauntless will and strength. The sixteenth sitting of the Council took place on August 9th of the same year and this is how presbyter Constantine of Apameia in Second Syria addressed the Council: 'I have come to your holy council to tell you that if I had been let to come and speak, we should have suffered what we have been through in the war with the Bulgarians. Because I wanted, from the very beginning of this council, to come and ask that peace be made, so that something be done to unite the two sides, and either be spared the misery, that is to say, both those who preach the single will and those who uphold the two wills'. It is asserted on the basis of this source that the decisive event occurred not earlier than March 18th and no later than August 9th of The year 681. The First Bulgarian Empire was able to defeat the Byzantine Empire in 811 and expand its territory eastward to the Black Sea, south to include Macedonia, and northwest to present-day Belgrade. The kingdom reached its greatest size under Tsar Simeon (893-927), who presided over a golden age of artistic and commercial expansion. After moving deep into Byzantine territory, Simeon was defeated in 924. Meanwhile, Rome and Byzantium competed for political and cultural influence in Bulgaria. The Eastern Empire won in 870 when Bulgaria accepted Eastern Rite (Orthodox) Christianity and an autocephalous Bulgarian Church was established. This decision opened Bulgaria to Byzantine culture (and territorial ambitions) through the literary language devised for the Slavs by the Orthodox monks Cyril and Methodius. Establishment of a common, official religion also permanently joined the Bulgarian and Slavic cultures.

After reaching its peak under Simeon, the First Bulgarian Empire declined in the middle of the tenth century. Byzantine opposition and internal weakness led to a loss of territory to the Magyars and the Russians. Bulgaria remained economically dependent on the Byzantine Empire, and the widespread Bogomil heresy opposed the secular Bulgarian state and its political ambitions as work of the devil. Seeking to restore a balance of power in the Balkans, the Byzantines allied with the Kievan Russians under Yaroslav and invaded Bulgaria several times in the late tenth century. Although the Bulgarians expanded their territory again briefly under Tsar Samuil at the end of the tenth century, in 1014 the Byzantines under Basil II inflicted a major military loss. By 1018 all of Bulgaria was under Byzantine control. For nearly two centuries, the Byzantines ruled harsh