The Avars were a Mongolian people. In the fourth century, they were one of many tribes to trouble the northern borders of the Chinese Empire. Little is known about the Avars in the period of their greatest power. Their base was situated somewhere near present-day Belgrade. By the end of the sixth century, their empire stretched from the River Volga to the Baltic Sea, and evidence suggests that they remained powerful well into the eighth century. They fought against the Byzantine Empire, and they reached as far as Constantinople, but could not take the city. Between 791 and 803, their kingdom was destroyed by the Franks and the Bulgarians, and the Avars merged with the Slavs.
The Bulgars or proto Bulgarians, were a herding people who fought their way westward from Asia, raiding for plunder in Constantinople’s empire in the Balkans during the rule of Justinian I, and then retreating. During the rule of the Byzantine emperor Constantine V, the Arab danger had abated, and Constantine felt free to attack the Bulgarians. However, by then, the Bulgarians had become powerful, and were able to withstand his attacks. Around 917 AD, Bulgaria became the centre of the Christian Slavic world. However, in 1018, the Byzantines attacked again, and destroyed the first Great Bulgarian Empire.