The Abbasid Caliphate was the third Islamic caliphate, founded in 750 CE, that succeeded the Umayyad Caliphate and lasted until the Mongol invasion in 1258 CE. It is significant for its establishment of a golden age of Islamic culture, where advancements in science, philosophy, and the arts flourished, and for its role in unifying the Muslim world under a more inclusive and culturally diverse regime.