From 9th century, the Abbasids state became weaker due to decline of Baghdad's control over distant provinces and continuous struggle between pro-Arab and proIranian groups in the army and bureaucracy. In 810, a civil war broke out between the supporters of two sons (Amin and Mamum) of the Caliph Harun-al-Rashid. This war created a new power block of Turkish slave officers. For the orthodoxy of power, the Shias started competing with Sunni. As a result of this, many new dynasties like Tahirid, Saminids and Tuluminds came into being.
As a result of this, the Abbasid power got limited to the areas of central Iraq and western Iran. The Buyids captured Baghdad in 945 CE, which ended Abbasid supremacy.