In August 1862 the worst massacre in U.S. history unfolded on the Minnesota prairie, launching what has come to be known as the Dakota War, the most violent ethnic conflict ever to roil the nation. When it was over, between six and seven hundred white settlers had been murdered in their homes, and thirty to forty thousand had fled the frontier of Minnesota. But the devastation was not all on one side. More than five hundred Indians, many of them women and children, perished in the aftermath of the conflict; and thirty-eight Dakota warriors were executed on one gallows, the largest mass...