Conversation so far:
What happened regarding the Vlachs in the 13th century?
In 1213 an army of Romans, Transylvanian Saxons, and Pechenegs, led by Ioachim of Sibiu, attacked the Bulgars and Cumans from Vidin.

Question: why did they attack them?
Self-contained rewrite: Why did the Romans, Saxons, and Pechenegs attack the Bulgars and Cumans?