First Bulgarian Empire

The First Bulgarian Empire (modern Bulgarian: Първo българско царство, Parvo Balgarsko Tsarstvo) was a medieval Bulgarian state founded in the north-eastern Balkans in c. 680 by the Bulgars, which subdued or drove out the local Byzantine population and made their allies the South Slavic settlers. At the height of its power it spread between Budapest and the Black Sea and from the Dnieper River in modern Ukraine to the Adriatic Sea. As the state solidified its position in the Balkans, it entered on a centuries-long interaction, sometimes friendly and sometimes hostile, with the Byzantine Empire. Bulgaria emerged as Byzantium's chief antagonist in the Balkans, resulting in several wars. The two powers however also enjoyed periods of peace and alliance, most notably during the Second Arab siege of Constantinople, where the Bulgarian army played a crucial role in breaking the siege. Byzantium had a strong cultural influence on Bulgaria, which also led to the eventual adoption of Christianity by Bulgaria in 864. After the disintegration of the Avar Khaganate, the Bulgarians expanded their territory up to the Pannonian Plain (in present-day Hungary). Later the Bulgarians confronted the advance of the Pechenegs and Cumans, and achieved a decisive victory over the Magyars, forcing them to establish themselves permanently in Pannonia.

During the late 9th and early 10th centuries, Tsar Simeon I achieved a string of victories over the Byzantines, and expanded the Bulgarian Empire to its apogee. After the annihilation of the Byzantine army in the battle of Anchialus in 917, the Bulgarians laid siege to Constantinople in 923 and 924. The Byzantines eventually recovered, and in 1014 under Basil II, inflicted a crushing defeat on the Bulgarians at the Battle of Kleidion. By 1018, the last Bulgarian strongholds had surrendered to the Byzantine Empire, and the First Bulgarian Empire had ceased to exist. It was succeeded by the Second Bulgarian Empire in 1185.

After the adoption of Christianity in 864 Bulgaria became the cultural center of Slavic Europe. Its leading cultural position was further consolidated with the invention of the Cyrillic script in its capital Preslav, and literature produced in the Old Bulgarian language soon began spreading North. Old Bulgarian became the lingua franca of Eastern Europe, where it came to be known as Old Church Slavonic. In 927 the fully independent Bulgarian Patriarchate was officially recognized. Later, as a reaction against Byzantine influences in the church, the influential Bogomil sect was born in Bulgaria in the mid-10th century.

Between the 7th and the 10th centuries, the local population, the Bulgars and the other tribes in the empire, which were outnumbered by the Slavs gradually became absorbed by them, adopting a South Slav language. Since the late 10th century, the names "Bulgarians" and "Bulgarian" became prevalent and became permanent designations for the local population, both in the literature and in the spoken language. The development of Old Church Slavonic literacy had the effect of preventing the assimilation of the South Slavs into neighboring cultures, and stimulating the formation of a distinct Bulgarian identity.