The Abbassid Caliphate does not represent a shift in the method of Islamic Leadership. The shift occurred between the last Rightly-Guided Caliph, 'Ali, and the first Umayyad Caliph, Mu'awiya. The position of Caliph shifted from being the person most devoted to the religion to a hereditary role, palaces and traditional trappings of imperial life took hold, and the Caliphate was firmly divided into wilayat (provinces) under the control of the wali'in (governors).
The only major change in policy that occurred under the Abbassids was that Mawali (Non-Arab Muslims) were now equal to Arab Muslims in terms of rights and privileges.
Abbasid Caliphate was created in 750.
Abbasid Caliphate.
Abbasid caliphate -- Baghdad Ummayyad Caliphate- Cordoba
Damascus was the capital of the Uymmad Caliphate, the caliphate before the Abbasid one. The first capital of the Abbasid Caliphate was Kufa, then Baghdad, then Samarra, and then Baghdad once more (all four cities located in Iraq).
The Abbasid dynasty
before
Harun Al Rashid
The first Caliph Abou Bakr, then Omar. then Othman, then Aly
The Muslim Empire established by second Rashidoon Caliph Hazrat Umar RAU, the Ummayad Caliphate, The Abbasid Caliphate in Baghdad, and the Ummayad Caliphate in Spain
The last Abbasid caliph was Al-Mustakfi Billah, who ruled from 1517 until the fall of the Abbasid Caliphate after the Ottoman conquest of Baghdad. Following this event, the Abbasid title continued in a nominal sense under Ottoman protection, but the political power of the caliphate effectively ended. The Abbasid lineage persists in a cultural and historical context, but Al-Mustakfi is generally recognized as the final caliph of the Abbasid dynasty.
The Abbasid dynasty established their caliphate in Baghdad, which became the capital in 762 CE. The choice of Baghdad was strategic, as it was located at the crossroads of trade routes and offered a central position in the Islamic world. Under the Abbasids, the caliphate flourished culturally, scientifically, and economically, marking a golden age of Islamic civilization.
Some of the lasting accomplishments of the Umayyad and Abbasid empires were religious freedom, lower taxes, and the geographical growth of the caliphate.