First Bulgarian Empire

The First Bulgarian Empire was a medieval state that existed in Southeastern Europe between the 7th and 11th centuries AD. It was founded in 680–681 after a group of Bulgars, led by Asparuh, moved south to the northeastern Balkans, and secured Byzantine recognition and their right to settle south of the Danube by defeating – possibly with the help of local South Slavic tribes – the Byzantine army led by Constantine IV. During the 9th and 10th century, Bulgaria reached the height of its power and stretched from the Danube Bend to the Black Sea and from the Dnieper River to the Adriatic Sea, becoming a major power capable of competing with the Byzantine Empire.

As the state solidified its position in the Balkans, it entered into a centuries-long interaction, sometimes friendly and sometimes hostile, with the Byzantine Empire. Bulgaria became Byzantium's primary threat to its north, resulting in several wars. The two powers also enjoyed periods of peace and cooperation, most notably the alliance during the Second Arab Siege of Constantinople, where the Bulgarian army broke the siege and destroyed the Arab army, thus preventing an Arab invasion of Southeastern Europe. Byzantium had a strong cultural influence on Bulgaria, which also led to the eventual adoption of Christianity in 864. After the disintegration of the Avar Khaganate, Bulgaria expanded its territory northwest to the Pannonian Plain. Later the Bulgarians confronted the advance of the Pechenegs and Cumans, and achieved a decisive victory over the Magyars, forcing them to settle permanently in Pannonia.

The ruling Bulgars and other non-Slavic tribes in the empire gradually mixed and adopted the prevailing Slavic language, thus gradually forming the Bulgarian nation from the 7th to the 10th century. From the 10th century, the demonym Bulgarian gained prevalence and became a permanent designation for the local population, both in literature and in common parlance. The development of Old Church Slavonic prevented the assimilation of the South Slavs into neighbouring cultures, and helped to create a distinct Bulgarian identity.

After the adoption of Christianity, Bulgaria became the foremost cultural and spiritual centre of Slavic Europe. Bulgaria's position as a leading cultural power was further strengthened by the adoption of the Glagolitic alphabet and the invention of the Early Cyrillic alphabet in the capital Preslav. The literature produced in Old Church Slavonic soon began to spread north, leading to Old Church Slavonic becoming the lingua franca of much of Eastern Europe. In 927, the fully independent Bulgarian Patriarchate was officially recognized.

During the late 9th and early 10th centuries, Simeon I achieved a string of victories over the Byzantines. Thereafter, he was recognized by the title tsar (caesar), and proceeded to expand the empire to its greatest territorial extent. 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 siege failed however, and the Bulgars were forced to retreat. The Bulgarians suffered a brutal invasion by Sviatoslav I Igorevich, the Grand-Prince of the Kievan Rus between 967 and 969, resulting in the empire becoming a vassal of the Rus. However, Sviatoslav was killed in 972, allowing the empire to briefly recover, although it was unable to reclaim the lost territories north of the Danube, in Thrace and Southern Macedonia. Their old rivals, the Byzantines, eventually recovered, and in 1014, under Basil II "the Bulgar Slayer", a crushing defeat was inflicted on the Bulgarians at the Battle of Kleidion, with Basil famously ordering the 15,000 Bulgarian prisoners to be blinded, with every 100th soldier spared one eye to guide the rest back home, forcing their families to support them for the rest of their lives. 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.