state. The Seljuks dominated a wide area from Asia Minor to the western sections of Transoxiana in the 11th century. The Seljuk Empire then split into states ruled by various local Turkic and Iranian rulers. The culture and intellectual life of the region continued unaffected by such political changes, however. Turkic tribes from the north continued to migrate into the region during this period. The power of the Seljuks however became diminished when the Seljuk Sultan Ahmed Sanjar was defeated by the Kara-Khitans at the Battle of Qatwan in 1141. Turkic words and terms characteristic of the literature of the 11th century are used in the modern Bukhara dialect of the Uzbeks. In the late 12th century, a Turkic leader of Khorazm, which is the region south of the Aral Sea, united Khorazm, Transoxiana, and Iran under his rule. Under the rule of the Khorazm shah Kutbeddin Muhammad and his son, Muhammad II, Transoxiana continued to be prosperous and rich while maintaining the region's Perso-Islamic identity. However, a new incursion of nomads from the north soon changed this situation. This time the invader was Genghis Khan with his Mongol armies. Mongol period The Mongol invasion of Central Asia is one of the turning points in the history of the region. The Mongols had such a lasting impact because they established the tradition that the legitimate ruler of any Central Asian state could only be a blood descendant of Genghis Khan. The Mongol conquest of Central Asia, which took place from 1219 to 1225, led to a wholesale change in the population of Mawarannahr. The conquest quickened the process of Turkification in some parts of the region because, although the armies of Genghis Khan were led by Mongols, they were made up mostly of Turkic tribes that had been incorporated into the Mongol armies as the tribes were encountered in the Mongols' southward sweep. As these armies settled in Mawarannahr, they intermixed with the local populations which did not flee. Another effect of the Mongol conquest was the large-scale damage the soldiers inflicted on cities such as Bukhara and on regions such as Khorazm. As the leading province of a wealthy state, Khorazm was treated especially severely. The irrigation networks in the region suffered extensive damage that was not repaired for several generations. Many Iranian-speaking populations were forced to flee southwards in order to avoid persecution. Following the death of Genghis