Answer:
B. U.S. troops attacked a village of peaceful Cheyenne and Arapaho Indians.
Step-by-step explanation:
This massacre was of peaceful Cheyenne and Arapaho peoples, led by Colonel John Chivington. It occurred because of the struggle for control for the Great Plains of eastern Colorado, which supposedly had an abundance of gold and other resources in the Rocky Mountains nearby. While this movement was initially praised, the attack was eventually condemned when the circumstances were revealed.