Krum against the Avars

At the beginning of his reign, Krum faced conflicts between the Avars and the Byzantine and Frankish empires. The two empires sought world domination, while the Avar Khaganate had once almost captured Constantinople. Krum launched a major operation to increase Bulgaria's power, wealth and territory. A second principal objective was to unite the Slavic tribes under Bulgarian rule and prevent their assimilation into Byzantine culture. Warfare with the Franks had considerably weakened the Avars, and Krum exploited this by attacking them.

He conquered Transylvania and lands in modern Hungary as far as the Tisza and united the South Slavs within Bulgaria.