In the year A.H. 536 (1141) Ye-liu Ta-shi died without male issue, and the empire of the Kara-Khitāys fell to two princesses in succession,[315] the daughter and the sister of the late ruler. It was in this year that Atsiz invited, or rather encouraged, the Kara-Khitāys to push their conquests farther west into Transoxiana. Sanjar, hearing of their advance, crossed the Oxus at the head of 100,000 men to meet them.[316] In the battle which ensued, in the valley of Dirgham, Sanjar met with the most crushing defeat which the Moslems had yet endured in their struggles against the infidels in the East.[317] Sanjar himself, who had hitherto been invincible, fled to Khorāsān by way of Tirmiz, accompanied by the remnants of his huge army. Transoxiana was now in the entire possession of the Kara-Khitāys, and for the first time a Mohammedan community became subject to the enemies of their faith.[318] The Kara-Khitāys, in the same year,[319] pushed on as far as Sarakhs, Merv, and Nīshāpūr, but they appear to have retired satisfied with the Oxus as their western boundary. Meanwhile Atsiz took advantage of Sanjar’s fallen fortunes, and began to ravage Khorāsān. The Sultan, however, had mustered forces sufficient to reassert his authority. He marched on the town of Khwārazm and invested it, whereon Atsiz bought him off with rich presents and assurances of good conduct in the future, A.H. 538 (1143).[320] This truce was of short duration. In the year A.H. 541 (1147) Sanjar again attacked Atsiz, but a permanent reconciliation was soon attained.[321] In A.H. 551 (1156)[322] Atsiz died at the age of sixty-one, and was succeeded by his son Il-Arslān, with whom the independent dynasty of Khwārazm-Shāhs properly begins. Meanwhile the affairs of Sultan Sanjar were going from bad to worse, and the end of the last great Seljūk was as ignoble as his career had been glorious. Strange to say, his ultimate ruin was caused by a Turkish tribe who came of the same stock as the Seljūks themselves.