First Bulgarian Empire (7th – 9th c.)
The Bulgarians (Turkic origin, later slavicized) moved from their homeland in Central Asia and settled at the mouth of the Danube in today’s southern Russia and Bessarabia in the middle of the 7th century. The Bulgarian invasions in the Byzantine territory did not represent any greater threat until they crossed the Danube and permanently settled between the Danube River and the Balkan mountains. The Byzantine Empire was at the time helpless against the Bulgarians who managed to subjugate the Slavic population.
The Bulgarians were slavicized and assimilated with the Slavic population over the next two centuries but they kept their name. They also remained the ruling class and established the First Bulgarian Empire in 682 which was also recognized by the Byzantine Empire. The First Bulgarian Empire developed into a important power in the Balkans during the reign of Khan Asparuh and his successors, especially during the rule of Khan Krum (802-814) and his son Omurtag (814-831). They expanded the frontiers of the Bulgarian Empire to the territory of former Avar state east of the Tisza river and captured Sofia from the Byzantine Empire.