Fourth Fitna

The Fourth Fitna or Great Abbasid Civil War involved conflict between the brothers al-Amin and al-Ma'mun over the succession to the throne of the Abbasid Caliphate. Their father, Harun al-Rashid, had named al-Amin as the first successor, but had also named al-Ma'mun as the second, with Khurasan granted to him as an appanage, while a third son, al-Qasim, had been designated as third successor. After Harun died in 809, al-Amin succeeded in Baghdad. Encouraged by the Baghdad court, al-Amin began trying to subvert the autonomous status of Khurasan; Qasim was quickly sidelined. In response, al-Ma'mun sought the support of the provincial élites of Khurasan and made moves to assert his own autonomy. As the rift between the two brothers and their respective camps widened, al-Amin declared his own son Musa as his heir and assembled a large army. Al-Amin's troops marched towards Khurasan, but al-Ma'mun's general Tahir ibn Husayn defeated them in the Battle of Rayy, and then invaded Iraq and besieged Baghdad itself. The city fell after a year, al-Amin was executed, and al-Ma'mun became Caliph, but he remained in Khurasan and did not come to Baghdad.