In the thirteenth century still another threat to the Muslim world appeared in the land beyond the Oxus: the Mongols. Led by Genghis Khan, a confederation of nomadic tribes which had already conquered China now attacked the Muslims. In 1220 they took Samarkand and Bukhara. By mid-century they had taken Russia, Central Europe, northern Iran, and the Caucuses, and in 1258, under Hulagu Khan, they invaded Baghdad and put an end to the remnants of...