For many years, Mongolian migrants have been plundering the caravans. But the style of their life changed in Temujin (Genghis Khan) era. After the unification of all the Mongol tribes, Genghis noticed the world outside, China and Iran were two neighbors of the Mongol-dominated lands. At first, Genghis sent ambassadors to Iran to facilitate trade with Iran, but the warden of Otrar (the border city in the Khwarezmian era) killed all Mongolian emissaries. At that time, there was no unified dynasty in Iran, but the Khwarezmid dynasty dominated most regions of Iran. Khwarezmians were the last dynasty of the Turk tribes in Iran, which after the killing of the Mongolian messengers by the ruler of the Otrar, Genghis attacked Iran and exterminated them.
Totally, the Mongols conquests Iran twice, these people looted and destroyed Iran during the first Mongol invasion in Iran, they burned libraries and anything that was associated with civilization in some way, and then returned to Mongolia. The second phase of the Mongol invasion in Iran began with the conquest of eastern regions and then all by Hulagu Khan (Genghis’s grandson). But this time because of the conflicts between Genghis deputies, they decided to remain in Iran. Soon the Mongols who inhabited Iran establish the Ilkhanate dynasty. Like previous non-Iranian dynasties, Iranian scientists and ministers came to the service of the Ilkhanates and helped them in the administration of the dominated lands. Great Iranian celebrities at this time were Nasir al-Din Tusi and Rashid al-Din Fadlullah Hamedani.