The Abbasid Caliphate (Arabic: العبّاسيّون, al-‘Abbāsīyūn) was the third of the Islamic Caliphates of the Islamic Empire. It was ruled by the Abbasid dynasty of caliphs, who built their capital in Baghdad after overthrowing the Umayyad caliphs from all but Al Andalus.
It was founded by a descendant of Muhammad's youngest uncle, Abbas ibn Abd al-Muttalib. It was created in Harran in 750 C.E. and shifted its capital in 762 C.E from Harran to Baghdad. It flourished for two centuries, but slowly went into decline with the rise to power of the Turkish army it had created, the Mamluks. Within 150 years of gaining power across Persia, they were forced to cede power to local dynastic amirs who only nominally acknowledged their power, and had to cede Al Andalus to an escaped Umayyad royal and the Maghreb and Ifriqiya to independent entities such as the Aghlabids and the Fatimids.
Their rule was briefly ended for three years in 1258, when Hulagu Khan, the Mongol conqueror, sacked Baghdad, resuming in Egypt in 1261. They continued to claim authority in religious matters from their base in Mamluk Egypt up to 1519 when power was formally transferred to the Ottomans and the capital transferred to Istanbul.