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.