The Abbasid Caliphate (الخلافة العباسية) was the third Islamic dynasty following the Umayyad Dynasty (الخلافة الأموية). The word Abbasid is derived from the name of prophet Muhammad’s uncle, Al-‘Abbas ibn ‘Abd al-Muttalib. The Abbasids opposed the Umayyads and tried to weaken their power by gaining the favor of groups who opposed them, especially the Shiites.
Abu al-‘Abbās ‘Abdu’llāh as-Saffāh (أبو العباس عبد الله السفاح) organized a rebellion against the Umayyads in Iran and Khurasan In 750. He defeated the Umayyads and was proclaimed Caliph on the Greater Zab River. After that, he eliminated the Umayyads and removed other opposition including the former Shiite allies. The Abbasids moved the capital city from Damasus to Iraq where there was less support for the Umayyads. Caliph Abu Ja’far Al-Mansur (أبو جعفر المنصور) founded Baghdad city in 762 to be the capital of the Abbasid empire. The Abbasid caliphate flourished for two centuries, with great rulers who expanded the empire and paid a lot of attention to literature, science and translation.
By the middle of the 8th century Baghdad became an important centre for learning and science. The House of Wisdom (بيت الحكمة) was built in Baghdad to be a major library and centre for translation. Major books in all languages known at that time were translated into Arabic. Harun al-Rashid (هارون الرشيد) is considered the most famous Abbasid Caliph. His reign was characterized by advancements in all fields. Muslim scholars and scientists benefited from the works translated from different languages at the time of the Abbasids. Major developments achieved at that age included development of mathematical, geometric and astronomical knowledge. Al-khwārizmī invented Algebra. In addition, scientists and physicians developed the areas of science and medicine such as anatomy, description of various diseases and their treatment, etc.
Various factors contributed to the decline of the Abbasid dynasty including power rivalry between eligible heirs to the caliphate, the rise to power of the Mamluks, i.e. Turkish officers appointed in Muslim armies, and external threats of the Byzantine Empire and the Mongols. The Abbasid rule was ended in 1258 at the hands of Hulagu Khan, the Mongol conqueror.