The destruction of a great Mongolian Empire by the revolt of its Turkish vassals (552) led to a westward flight of the vanquished, known to the Chinese as the Juan-juan, to the West as the Avars.
The Avars moved to the Russian steppes, where the Byzantine emperor Justinian paid them to subjugate the Huns and Slavs who had been raiding Roman provinces in the Balkans.
The empire of the Avars peaked at the end of the 6th century when it reached from the Volga to the Danube. They were partly responsible for the southward migration of the Serbs and Croats.
The Avar state, weakened by internal dissent, was destroyed by a combined Frankish and Bulgarian attack in 796.