Most people call what happened that day in 1864 a massacre. But a firsthand account from a soldier simply calls it war. This morning in a grassy valley in eastern Colorado, members of the Cheyenne and Arapaho tribes and officials from the National Park Service will formally dedicate the Sand Creek Massacre National Historic Site. At the same time, the Old Colorado City Historical Society will rerelease an out-of-print book that argues that the massacre wasn’t a massacre at all. “I realize even suggesting that isn’t very popular, but things aren’t as simple as they are made out to be,”...