Complex sentence: An armed conflict starts between the rival Muslim caliphs Al-Musta'in and Al-Mu'tazz, they fight to determine who would gain control over the Abbasid Caliphate (until 866).
Split into simpler sentences: An armed conflict starts between the rival Muslim caliphs Al-Musta'in and Al-Mu'tazz. They fight to determine who takes control over the Abbasid Caliphate (until 866).