Chingiz had been occupied since the overthrow of the Naimans with the conquest of China, and “though it was reserved for his grandson to complete the subjugation of the Celestial Empire,[367] a great part of the northern provinces ... was added to the Mongol dominions during the great Khān’s own lifetime.”[368] In 1218 he despatched an army 20,000 strong, under Noyan Chebe, to attack Guchluk Khān in Kāshghar. Hearing of their approach, Guchluk fled, but was shortly afterwards overtaken in the mountains of Badakhshān and put to death. He was, as we have seen, a bigot, and especially intolerant in his dealings with Mohammedans. The Mongols proclaimed religious liberty, and thereby ensured for themselves the favour of the people.[369] After the downfall of the Kara-Khitāys the possessions of Mohammad of Khwārazm extended into the heart of Turkestān, with Samarkand as a capital. Those of Guchluk Khān were restricted to Kāshghar, Khotan, and Yarkand.[370] Chingiz’s relations with his powerful neighbour in Khwārazm were long of a peaceful and even friendly nature, but causes were at work which altered them radically.[371] Abū-l-Ghāzi states[372] that the Caliph Nāsir’s intense jealousy of the northern empire led him to adopt every means in his power to weaken it, and that he invited Chingiz to attack Sultan Mohammad. It is probable that this perfidious policy caused a coldness between the two potentates; but the immediate cause of rupture was an act for which the Khwāarazm Sultan was alone responsible. He cruelly slew, at Otrār, some Mohammedan traders who had incurred his animosity, in spite of the fact that they were travelling under Chingiz’s protection. The avalanches which descended on the habitable world in the twelfth century were thus set in motion by princes whose interest required that the vast forces controlled by Chingiz should remain pent up in their native steppes. In A.H. 615 (1218) he set out for Otrār, determined to avenge the insult offered by Sultan Mohammad, and on his way was joined by large reinforcements of Karliks, Uïghūr and other Mongol tribes, eager to share in the plunder of the West.[373] On reaching that goal he divided his forces among his sons, and laid down for each the object of attack.