A Neglected Cause of the Sioux Uprising

After discussing briefly the larger causes of the 1862 Sioux Uprising, including unfair treaties an the loss fo Sioux lands, the author goes on to explore the idea that the U.S. Civil War played a role in convincing the Sioux to rebel. He suggests that the Civil War demonstrated that the authority of the Union could be challenged and, in addition, that many of the "able-bodied" men in the valley had enlisted, leaving citizens who might be viewed as more vulnerable to attack.