In the New York Times, Ned Blackhawk reminds us, “It’s the 150th anniversary of one of the most appalling massacres of Indians ever.”
In terms of sheer horror, few events matched Sand Creek. Pregnant women were murdered and scalped, genitalia were paraded as trophies, and scores of wanton acts of violence characterize the accounts of the few Army officers who dared to report them. . . .
Sand Creek, Bear River and the Long Walk remain important parts of the Civil War and of American history. But in our popular narrative, the Civil War obscures such campaigns against American Indians. In fact, the war made such violence possible . . .
See the full article here. There are more details in the Smithsonian Magazine, and a few sources from the time here.