Tahirid dynasty
Upon Al-Amin's death, Al-Ma'mun became Caliph. Al-Ma'mun extended the Abbasid empire's territory during his reign and dealt with rebellions. Al-Ma'mun had been named governor of Khurasan by Harun, and after his ascension to power, the caliph named Tahir as governor of his military services in order to assure his loyalty. Tahir and his family became entrenched in Iranian politics and became powerful, frustrating Al-Ma'mun's desire to centralize and strengthen Caliphal power. The rising power of the Tahirid dynasty became a threat as Al-Ma'mun's own policies alienated them and other opponents.