The First Bulgarian Empire is a medieval Bulgarian state founded in the north-eastern Balkans in c. 680 by the Bulgars, which subdues or drives out the Byzantines and makes 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 on 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 enjoy 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.After the adoption of Christianity in 864, Bulgaria becomes the cultural center of Slavic Europe.

Its leading cultural position is further consolidated with the invention of the Cyrillic script in its capital Preslav, and literature produced in the Old Bulgarian language soon begins spreading North.

Old Bulgarian becomes the lingua franca of Eastern Europe, where it comes to be known as Old Church Slavonic.

In 927, the fully independent Bulgarian Patriarchate is officially recognized.Between the 7th and 10th centuries, the local population, the Bulgars and the other tribes in the empire, which are outnumbered by the Slavs, gradually become absorbed by them, adopting a South Slav language.

From the late 10th century, the names Bulgarians and Bulgarian become prevalent and become permanent designations for the local population, both in the literature and in the spoken language.

The development of Old Church Slavonic literacy has the effect of preventing the assimilation of the South Slavs into neighboring cultures, while stimulating the formation of a distinct Bulgarian identity.During the late 9th and early 10th centuries, Tsar Simeon I achieves a string of victories over the Byzantines, and expands the Bulgarian Empire to its apogee.

After the annihilation of the Byzantine army in the battle of Anchialus in 917, the Bulgarians lay siege to Constantinople in 923 and 924.

The Byzantines eventually recover, and in 1014 under Basil II, inflict a crushing defeat on the Bulgarians at the Battle of Kleidion.

By 1018, the last Bulgarian strongholds have surrendered to the Byzantine Empire, and the First Bulgarian Empire has ceased to exist.

It was succeeded by the Second Bulgarian Empire in 1185.