As a mark of respect for his enemy's bravery, the Khan ordered his archers not to fire, and so the Shah managed to gain the opposite bank; however, his family and nearly all his army were slaughtered.

[a] Shah Muhammad II, wary of Mongol skill in battle and doubtful of his commanders' loyalties, adopted a defence in depth strategy based on garrisoning his cities, especially Otrar, Samarkand and Gurganj.

[3] However, the Khan demonstrated superior strategic ability, splitting the Shah's forces to take Bukhara in February 1220 and Samarkand in March; the border town of Otrar held out for six months until it fell in April.

[4] Genghis sent a 30,000 to 40,000 strong Mongol army led by Jebe and Subutai to hunt down the Shah, who had begun to flee west with his eldest son Jalal al-Din.

[5][6] The Mongol army sacked numerous cities during their long pursuit, including Tus, Qazvin and Ardabil;[7] however, the Shah found refuge on an island in the Caspian Sea, where he died in December 1220.

[9] Discovering a plot against his life, Jalal al-Din left the city and set out southwards across the Karakum Desert, emerging near Nisa where he defeated a Mongol detachment.

[13] Jalal al-Din narrowly escaped being caught at Nishapur, where he had hoped to raise an army; he evaded his pursuers and managed to reach Bost, where his maternal uncle Amin Malik joined him with a reasonable force.

[14] The Shah then moved to Ghazni, where many Khwarazmian loyalists, including Qurlaq, Khalaj and Turkmens, joined him and within a few weeks he had amassed a well-equipped, if not firmly united, army of around 65,000 soldiers.

[22] The Mongols sent detachments ahead to seize several passes that led from Ghazni to Peshawar, so when the deserters under Ighrak finally decided to rejoin Jalal al-Din, he found the way barred.

[28] Genghis deployed his forces in a crescent-shape, pinning the Khwarazmians against the river; he personally commanded the reserve to make sure the Shah wouldn't be able to break through the Mongol lines and escape.

[27][28] Although many men were lost during Bela Noyan's climb, the Mongol detachment successfully scaled the ridge and attacked the Shah's left wing from the flank and rear.

[32] Jalal al-Din managed to collect the survivors of his army; displaying his military acumen, he defeated local rulers and started establishing a small state in India.