Primary empires were the product of internal development and self-sustaining through the exploitation of their own resources, but there were also historically a large number of “shadow empires.” These were imperial polities that were the products of secondary empire formation, which came into existence as a response to the formation of primary empires elsewhere and could not exist except in interaction with them. One unusual subset of these were “empires of nostalgia” that claimed an imperial tradition and the outward trappings of an extinct empire, but did not themselves meet the basic requirements of an imperial state such as direct control of territory, true centralized rule, or significant urban centers. The most famous European example was the Carolingian Empire established by Charlemagne and its long lived successor, the Holy Roman Empire, which survived as an institution for a thousand years. The Islamic State’s proclamation of itself as a reborn caliphate is now a contemporary example built on nostalgia in the Islamic world for a long-dead empire that still exerts a strong cultural attraction upon many Muslims. The Islamic State justifies its actions and ideologies by attempting to ground them in a lost golden age that they propose to restore
