The Otrar Catastrophe was a siege that took place between December 1219 and February 1220 during the Mongol conquest of the Khwarazmian Empire at Otrar, a large trading city on the Syr Darya river. Inalchuq, the city's governor, had seized the goods of a Mongol trade caravan the previous year; after more provocations from Inalchuq's liege and ruler of the Khwarazmian Empire, Shah Muhammad II, Genghis Khan launched a full-scale invasion of the empire.