Answer: B. decades of war along the Great Plains
Explanation:
The Sand Creek Massacre of 1864 happened when soldiers under the command of U.S. Army Colonel John Chivington attacked a peaceful Indian village and killed between 200 and 500 Indians and then mutilated their corpses.
This massacre had a profound effect on the Native and American relationship at the time which was already strained. The massacre reduced the power of those Natives who wanted peace and led to retaliatory attacks by more war prone Natives who raided various settlements as well as decades of war such as the Great Sioux War and the Battle of the Little Bighorn.