al-Mustaḍīʾ bi-amr Allāh

During the ten-year reign of al-Mustadi bi-amr Allah, caliph in Baghdad from 1170 to 1180, the Abbasid house recovered a symbolic prize it had lost two centuries earlier: recognition in Egypt. He was a son of al-Mustanjid and succeeded him at a time when the caliphs once again ruled Iraq as a territorial state, having emerged from Seljuk tutelage in the previous generation.

The defining event of the reign occurred far from Baghdad. In 1171 Saladin, then vizier of Egypt for the Syrian ruler Nur al-Din, allowed the Fatimid caliphate to lapse on the death of its last caliph, al-Adid, and ordered the khutba, the Friday sermon, in Cairo to be pronounced in the name of al-Mustadi. The change ended more than two hundred years of Ismaili Shia rule in Egypt and restored the country, in name at least, to Abbasid Sunni allegiance for the first time since 969. The caliph's name on Egypt's pulpits and coinage was a momentous gain in prestige, even though Baghdad exercised no actual control there.

The reordering of the Muslim Near East continued through the decade. Nur al-Din died in 1174, and Saladin moved into Syria, building the power that would later confront the Crusader kingdom; he sought and received caliphal diplomas legitimising his rule over Egypt and the Syrian lands he acquired. For al-Mustadi, as for his father, the caliphate's influence beyond Iraq operated through such grants of legitimacy rather than through arms, while within Iraq his administration governed Baghdad and its dependent districts directly.

The chroniclers present al-Mustadi as a mild and generous ruler, favourable to the religious classes; the celebrated Hanbali preacher and historian Ibn al-Jawzi was prominent in Baghdad during his reign and wrote of him approvingly. Detailed information about his government is nonetheless limited, and the reign was short. He died in 1180, about forty years old, and was succeeded by his son al-Nasir li-Din Allah, the most forceful of the later Abbasids, whose long reign would carry the revived caliphal state to its furthest extent before the Mongol catastrophe of the following century.