The rule of this dynasty ended in 1258, when Baghdad fell to the Mongols.
Under the rule of this dynasty's ruler al-Mustakfi, its capital was siezed by the Buyids. The eighth ruler of this dynasty, al-Mutasim, was the first to employ Turkish mercenaries. This dynasty was founded when Abu Muslim defeated the last caliph of a preceding dynasty, Marwan II, at the battle of the Great Zab River, and it was once ruled by the legendarily opulent (*) Harun al-Rashid. The rule of this dynasty ended in 1258, when Baghdad fell to the Mongols. For 10 points, identify this second great Muslim dynasty, which overthew and succeeded the Umayyad caliphate in 750.
Under the rule of this dynasty's ruler al-Mustakfi, its capital was siezed by the Buyids.
{Abbasid} Dynasty [or {Abbasid} Caliphate]