«The Sunni-Shia divide came to be tremendously important during the later Middle Ages, particularly (as we shall see) during the crusading era. But it has lasted far longer than that. During the twentieth century, a revived, poisonous sectarianism established in part along Sunni-Shia lines began to inform world geopolitics—playing a role in the interconnected Iran-Iraq War, U.S.-led Gulf wars, and long-running “Islamic cold war,” which has pitted Saudi Arabia and Iran against one another for regional hegemony in the Middle East since 1979; as well as other, painful and deadly conflicts that have been fought in Pakistan, Iraq, and Syria. That all this can still be traced back to the machinations of powerful men in the seventh century a.d. may seem astonishing—but as so often proves the case, the Middle Ages remain with us today.

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