Final answer:
The war against the Khanate of Khwarazmia was triggered by the murder of Mongol traders and the subsequent mistreatment of Chinggis Khan's envoys sent to demand compensation from the Khwarazmian ruler.
Step-by-step explanation:
Trigger Event for the War Against the Khanate of Khwarazmia
The significant event that triggered the war against the Khanate of Khwarazmia was not an assassination of a neighboring ruler, a violation of a peace treaty, or trade route disputes. Instead, it was the murder of Mongol traders and the subsequent maltreatment of Chinggis Khan's envoys by the Khwarazmian ruler that led to a vengeance-filled war by the Mongol Empire. Initially, Chinggis Khan sought peaceful trade relations but was met with aggression, which the Khwarazmians would soon regret. The mistreatment and killing of the envoys was perceived as a grave provocation warranting a forceful response, and thus, in 1220, the Mongols launched a devastatingly successful military campaign against the Khwarazmian Empire.