The debate over how to think about the Islamic State group has mainly centered on important but abstruse questions — is it evil or not? — and on what combination of military and economic pressure might be necessary to prevent the establishment of a caliphate.

What the debate is lacking is a sense of history. And the historical antecedents do supply an early analogy to Islamic State: a warrior people who came out of nowhere, defeated mightier forces in battle, accumulated wealth and, in their bloody ferocity, terrified every civilization with which they came into contact.

I refer to the steppe nomads.