The Byzantine–Bulgarian wars were a series of conflicts fought between the Byzantines and Bulgarians
which began when the Bulgars first settled in the Balkan peninsula in the 5th century, and intensified with the expansion of the Bulgarian Empire
to the southwest after 680 AD. The Byzantines and Bulgarians
continued to clash over the next century with variable success, until the Bulgarians
, led by Krum, inflicted a series of crushing defeats on the Byzantines.