The Abbasids revolt was centered over the lack of representation from the mawali (converted), the influence exerted by regions traditionally identified with the Byzantines, and the use of the Byzantine bureaucratic framework.
After deposing the Ummayad, one radical change was the use of Arabic as lingua franca was imposed over the empire. This was initiated by the Ummayads, but with the Abbasids was finally complete. Therefore, the identity of Islam was based on membership to the umma and the language. That is the reason why the Empire survived as an entity for another 200 years until the contradictions between classes and the atomization of power emptied the Caliphate from real political power.
