The Iranians were always given special importance by the Abbasid rulers, since their chief partisans such as Abu Muslim Khorasani, the Barmakids and the family of sahl and Taher Zu'l-Yaminain were Iranians.Mamun's own mother Marajel was an Iranian in his fight against his step brother Amin, he selected Khorasan as the seat of his caliphate, with Merv (in present day Turkmenistan) as his capital

Mamun, however, was faced with a very tense political crisis.After  the defeat and killing of Amin, the Alavis, feeling respite from the frequent persecutions and tortue of the caliphs, and realizing that the new capital, Merv, was in far away Khorasan, felt secure enough to start their revolutionary  activities throughout the Islamic lands against Abbasid rule.In addition to this, in Baghdad, some of Amin's die-hard followers were strongly against Mamun.