A divided Islamic world offered feeble resistance to the Crusaders who consolidated their hold on the eastern Mediterranean and imposed their fiefdoms on the region. The Seljuks, preoccupied with defending their eastern flank against the Afghan Ghaznavids, had thinned out their western defenses. The pagan Turkish tribes across the Amu Darya on the northeastern frontiers were a constant menace....

It was the century when three powerful traditions-Islamic, Medieval Christian and Mongol-collided. The aftermath of this collision transformed all three traditions in ways that were profound and basic. The cataclysm of the Mongols was a global event, which left its indelible mark upon human history. It destroyed ancient dynasties, remade human races and fundamentally changed the way people...