Complex sentence: The Khazars even laid siege to Warthan, during which they employed mangonels, a fact which, according to K.Y. Blankinship, shows that the Khazars were "a militarily sophisticated nation, not a mere disorganized pack of barbarians".
Split into simpler sentences: The Khazars even laid siege to Warthan, during which they employed mangonels. The use of such advanced siege machines shows, according to K.Y. Blankinship, that the Khazars were "a militarily sophisticated nation, not a mere disorganized pack of barbarians".