On October 10, 680, Husain Ibn Ali, grandson of the prophet Muhammad, and a small band of followers were attacked at Karbala, in what is now Iraq, by a much larger force under the command of the reigning Caliph Yazid I. At stake was the leadership of the Islamic world. What ensued was less a battle than a slaughter. All of Husain’s supporters were killed. Seventy-two of them were beheaded.

Husain himself was, according to tradition, the last to fall. His corpse was then also decapitated, and his body trampled under horses so as to be unrecognizable. The day of his death has been celebrated ever since by the descendants of his followers, the Shia, as Ashura. It is a day of mourning and vows of retribution.

It has been 1336 years. It might as well have been yesterday.

Days ago, Qais Al-Khazaali, leader of the Shia militia Asaib Ahl al-Haq, vowed that the Iraqi offensive to retake the city of Mosul would be “revenge for the killing of Imam Husain.” The implication was clear. The attacking Iraqi force, excluding the Kurdish Peshmerga, is overwhelmingly Shia. Mosul is a predominately Sunni city populated in Shia eyes by the descendants of Yazid I, and thus sharing in his guilt.