How Did The Iranians Expel The Mongols From Iran?

  The Mongol invasion of Iran began in 1219 after two diplomatic missions to Khwarezm sent by Genghis Khan had been massacred. During 1220–21 Bukhara, Samarkand, Herat, Tus, and Nishapur were razed, and the whole populations were slaughtered. The Khwarezm-Shah fled, to die on an island off the Caspian coast. During the invasion of Transoxiana in 1219, along with the main Mongol force, Genghis Khan used a Chinese specialist catapult unit in battle, they were used again in 1220 in Transoxania. The Chinese may have used the catapults to hurl gunpowder bombs since they already had them by this time