The Fourth Fitna or Great Abbasid Civil War Military_operation resulted Causation from the conflict Hostile_encounter between the brothers al-Amin and al-Ma'mun over the succession Change_of_leadership to the throne of the Abbasid Caliphate .

Their father , Caliph Harun al-Rashid , had named Name_conferral al-Amin as the first successor , but had also named Name_conferral al-Ma'mun as the second , with Khurasan granted Giving to him as an appanage .

In response Response , al-Ma'mun sought Hold the support Supporting of the provincial élites of Khurasan and made moves to assert Statement his own autonomy .

In 811 , al-Amin 's troops marched Self_motion against Khurasan , but al-Ma'mun 's general Tahir ibn Husayn defeated Conquering them in the Battle Hostile_encounter of Rayy , and then invaded Attack Iraq and besieged Besieging Baghdad itself .

The city fell after a year , al-Amin was executed Killing , and al-Ma'mun became Becoming Caliph .

In addition , the pro-Khurasani policies followed by al-Ma'mun 's powerful chief minister , al-Fadl ibn Sahl , and al-Ma'mun 's espousal of an Alid succession in the person of Ali al-Ridha , alienated Influence the traditional Baghdad élites , who saw themselves increasingly marginalized Cause_change_of_position_on_a_scale .

In addition , the pro-Khurasani policies followed by al-Ma'mun 's powerful chief minister , al-Fadl ibn Sahl , and al-Ma'mun 's espousal of an Alid succession in the person of Ali al-Ridha , alienated Influence the traditional Baghdad élites , who saw themselves increasingly marginalized Cause_change_of_position_on_a_scale .

Consequently , al-Ma'mun 's uncle Ibrahim was proclaimed Statement rival Caliph at Baghdad in 817 , forcing Request al-Ma'mun to intervene Response personally .

Consequently , al-Ma'mun 's uncle Ibrahim was proclaimed Statement rival Caliph at Baghdad in 817 , forcing Request al-Ma'mun to intervene Response personally .

Fadl ibn Sahl was assassinated Killing and al-Ma'mun left GiveUp Khurasan for Baghdad , which he entered Arriving in 819 .

The next years saw the consolidation Cause_to_amalgamate of al-Ma'mun 's authority and the re-incorporation of the western provinces against local rebels , a process not completed Process_end until the pacification Cause_to_make_progress of Egypt in 827 .

Historians have interpreted Protest the conflict Violence variously ; in the words of the Iranologist Elton L. Daniel , it has been regard as `` a conflict Violence over the succession between a rather incompetent , besotted Change_sentiment al-Amin and his shrewdly competent brother al-Ma'mun ; as the product Manufacturing of harem intrigues ; as an extension Expansion of the personal rivalry Competition between the ministers al-Fadl b. Rabi ' and al-Fadl b. Sahl ; or as a struggle Violence between Arabs and Persians for the control Control of the government '' .