Final answer:
The Sand Creek Massacre was triggered by conflicts over land encroachment on Native American reservation lands. A militia raid led by Colonel Chivington attacked a peaceful settlement, resulting in the deaths of many Native American women and children.
Step-by-step explanation:
The Sand Creek Massacre was triggered by the continuous encroachment on Native American reservation lands and growing conflicts between settlers and Native American tribes.
In Colorado, tensions escalated when settlers formed armed militias to fight against land encroachment by Arapahoe and Cheyenne tribes. Colonel John Chivington led a militia raid on a camp where the Cheyenne leader Black Kettle had negotiated a peaceful settlement.
Despite the camp flying both the American and white surrender flags, Chivington's troops attacked the camp, killing close to one hundred people, mainly women and children.