Byzantine–Bulgarian wars: Battle of Kleidion: Byzantine emperor Basil II inflicts a decisive defeat on the Bulgarian army, and his subsequent treatment of 15,000 prisoners reportedly causes Tsar Samuil of Bulgaria to die of a heart attack less than three months later, on October 6.

The Byzantine–Bulgarian wars were a series of conflicts fought between the Byzantine Empire and the Bulgarian Empire which began after the Bulgars conquered parts of the Balkan peninsula after 680 AD. The Byzantine and First Bulgarian Empire continued to clash over the next century with varying…