Complex sentence: Bulgaria's territory increased under Krum ("c." 803--814), who took Adrianople and forced at least 10,000 of the town's inhabitants to settle north of the Lower Danube in 813.
Split into simpler sentences: Bulgaria's territory increased under Krum ("c." 803--814). For instance, he took Adrianople, and forced at least 10,000 of the town's inhabitants to settle north of the Lower Danube in 813.