Compare the Sand Creek, Fetterman, and Wounded Knee massacres.

In stark contrast to the Sand Creek and Wounded Knee massacres, The Fetterman Fight was fought between soldiers. The Fetterman Fight, or the Fetterman Massacre, happened in Wyoming on December 21, 1866. Ten Native Americans lured union troops into an ambush. The eighty-one soldiers under the command of Captain William J. Fetterman found themselves overwhelmed by over 1,000 Lakota, Cheyenne, and Arapaho Indians. They killed all 81 soldiers. At the time it was an unprecedented defeat in the Great Plains.
Each event fell within a thirty-year period, bloody punctuations in the relationship between the United States and the Native American populations. The tragedies of Sand Creek and Wounded Knee resulted from broken treaties, seizure of land, and the overall dehumanization of Indian peoples.
On November 29, 1864, the Sand Creek Massacre occurred in the Southeastern Colorado Territory. Under US Army Colonel John Chivington, 675 men from the Colorado US Volunteer Cavalry destroyed a village of Arapaho and Cheyenne people. The soldiers killed between seventy and 500 Native Americans, two-thirds of whom were women and children.
The Wounded Knee Massacre took place in South Dakota on December 29, 1890. The US army had surrounded and was in the process of disarming a camp of Lakota Indians. Tensions were high, as a spiritual Ghost Dance was being performed, which some Americans interpreted as a war ritual. Additionally, a Lakota named Black Coyote resisted the seizure of his property. At some point, his rifle went off, and the US army opened fire. The Lakota fought back, but ultimately around 300 men, women, and children of the camp had died, with another fifty-one injured.
The Sand Creek and Wounded Knee massacres were both unprovoked attacks on vulnerable Native American communities. These were not armed battles between combatants. In both events, most of the slain were practically defenseless Native civilians. At Sand Creek, the village openly displayed their peaceful intentions by flying an American flag tied to a white flag. While the Fetterman Massacre resulted in a significant loss of life, it was not a surprise attack on an unarmed population.
http://plainshumanities.unl.edu/encyclopedia/doc/egp.war.056

https://www.nps.gov/sand/learn/historyculture/massacre.htm

https://www.wyohistory.org/encyclopedia/fetterman-battlefield