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 .

Encouraged Convincing by the Baghdad court , al-Amin began Process_start trying to subvert Change_of_leadership the autonomous status of Khurasan , and al-Qasim was quickly sidelined Process_end .

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 .

Al-Ma'mun chose Choosing to remain Temporary_stay in Khurasan , however , rather than coming to Motion the capital .

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

The Umayyads under the governor of Khurasan , Asad ibn Abdallah al-Qasri , had invaded Attack the principality of Khuttal in Transoxiana , and the local ruler Control called Request upon the Türgesh for aid Assistance .

The failure Earnings_and_losses of the Umayyad campaign Military_operation meant Statement the complete collapse of the Arab control Control in the Upper Oxus valley , and opened Openness Khurasan itself to the Türgesh .