In 632, Khan Kubrat united the three largest Bulgar tribes: the Kutrigur, the Utugur and the Onogonduri, thus forming the country that now historians call Great Bulgaria (also known as Onoguria). This country was situated between the lower course of the Danube river to the west, the Black Sea and the Azov Sea to the south, the Kuban river to the east and the Donets river to the north. The capital was Phanagoria, on the Azov.

In 635, Kubrat signed a peace treaty with emperor Heraclius of the Byzantine Empire, expanding the Bulgar kingdom further into the Balkans. Later, Kubrat was crowned with the title Patrician by Heraclius. The kingdom never survived Kubrat's death. After several wars with the Khazars, the Bulgars were finally defeated and they migrated to the south, to the north, and mainly to the west into the Balkans, where most of the other Bulgar tribes were living, in a state vassal to the Byzantine Empire since the 5th century.

Another successor of Khan Kubrat, Asparuh (Kotrag's brother) moved west, occupying today's southern Bessarabia. After a successful war with Byzantium in 680, Asparuh's khanate conquered initially Scythia Minor and was recognised as an independent state under the subsequent treaty signed with the Byzantine Empire in 681. That year is usually regarded as the year of the establishment of present-day Bulgaria and Asparuh is regarded as the first Bulgarian ruler.