The First Bulgarian Empire is a medieval Bulgarian state founded in the northeastern Balkans in c. 680 by the Bulgars, who subdue or drive out the Byzantines and make the South Slavic settlers their allies.

At the height of its power, it spreads between Budapest and the Black Sea and from the Dnieper River in modern Ukraine to the Adriatic Sea.

As the state solidifies its position in the Balkans, it enters into a centuries-long interaction, sometimes friendly and sometimes hostile, with the Byzantine Empire.

Bulgaria emerges 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 plays a crucial role in breaking the siege.

Byzantium has a strong cultural influence on Bulgaria, which also leads to the eventual adoption of Christianity by Bulgaria in 864.

After the disintegration of the Avar Khaganate, the Bulgarians expand their territory up to the Pannonian Plain (in present-day Hungary).

Later, the Bulgarians confront the advance of the Pechenegs and Cumans, and achieve a decisive victory over the Magyars, forcing them to establish themselves permanently in Pannonia.