During the Civil War, the Union Army forced the removal and four-year incarceration of the Navajo, resulting in the death of half their population. During the same time the Dakota Nation was forced by the Union Army out of their homeland in Minnesota, while unarmed Northern Cheyenne were massacred in their reservation at Sand Creek in Colorado. After the Civil War, six of the seven divisions of the US Army were stationed west of the Mississippi, where they carried out genocidal wars against the Plains and southwestern Indigenous nations, including the intentional extermination of tens of millions of bison. These troops were pulled out of the South, where they were supposed to be occupying the defeated former Confederate states to allow for land distribution to former slaves and for their political participation in democratic elections. Without sufficient US Army troops to stop them, the Ku Klux Klan made Reconstruction impossible, imposed a reign of terror, and restored the ex-Confederate elite.