They were! The Mongols were a true, global super power, on oar with Alexanders Macedons and ancient Rome.

In the very large set of "this was particularly nasty" things that make up the early middle ages, this one really stands out. I have little doubt that this siege and subsequent sacking effectively set back humanity as a whole - and for the sole and simple reason that the caliph sent a snooty reply back to the Mongols.