In 1218, following the mistreatment of Mongol ambassadors by Mohammed Shah, ruler of the Khwarizmian Empire, Genghis Khan mobilized his army. The Khwarizmian Empire spread across Turkestan, Persia and northern India. Like all Mongol campaigns, the invasion was preceded by a considerable effort on the part of the intelligence network. As he gathered information and made detailed invasion preparations, Genghis Khan concentrated his main forces east of Lake Balkhash on the Irtish River in 1219.