The First Bulgarian Empire was a medieval state
founded in the north-eastern Balkans in c. 681 by the Bulgars,
uniting with seven South Slavic tribes. 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 Khanate, 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.[7] 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 alphabet 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.