caliph an-Nasir . When the caliph rejected his claim, Ala ad-Din Muhammad proclaimed one of his nobles caliph and unnsuccessfully tried to depose an-Naisr. The Mongol invasion of Iran began in 1219, after two diplomatic missions to Khwarezm sent by Genghis Khan had been massacred. During 1220–21 Bukhara , Samarkand , Herat