Answer
The Drevlians were a Slavic tribe that lived in what is now the northern Ukraine. They were known for their fierce resistance to invaders, and Olga of Kiev was responsible for their subjugation in the 9th century. Olga led a campaign against the Drevlians after her husband, Prince Igor, was killed by them. The campaign was successful, and the Drevlians were forced to submit to Kievan rule.