Mohammed II
At this point, the Mongol army was divided into five widely separated groups on opposite ends of the enemy Empire. After the Shah did not mount an active defense of the cities on the Syr Darya, Genghis and Tolui, at the head of an army of roughly 50,000 men, skirted the natural defense barrier of the Syr Darya and its fortified cities, and went westwards to lay siege to the city of Bukhara first. To do this, they traversed 300 miles of the seemingly impassable Kyzyl Kum desert by hopping through the various oases, guided most of the way by captured nomads. The Mongols arrived at the gates of Bukhara virtually unnoticed. Many military tacticians regard this surprise entrance to Bukhara as one of the most successful maneuvers in warfare. Whatever Mohammed II was intending to do, Genghis's maneuver across his rear completely stole away his initiative and prevented him from carrying out any possible plans. The Khwarezm army could only slowly react to the lightning fast Mongol maneuvers.