During Harrison's administration, the Lakota Sioux, previously confined to reservations in South Dakota, grew restive under the influence of Wovoka, a medicine man, who encouraged them to participate in a spiritual movement called the Ghost Dance. Many in Washington did not understand the predominantly religious nature of the Ghost Dance, and thought it was a militant movement being used to rally Native Americans against the government. On December 29, 1890, troops from the Seventh Cavalry clashed with the Sioux at Wounded Knee. The result was a massacre of at least 146 Sioux, including many women and children; the dead Sioux were buried in a mass grave. In reaction Harrison directed Major General Nelson A. Miles to investigate and ordered 3,500 federal troops to South Dakota; the uprising was brought to an end. Wounded Knee is considered the last major American Indian battle in the 19th century. Harrison's general policy on American Indians was to encourage assimilation into white society and, despite the massacre, he believed the policy to have been generally successful. This policy, known as the allotment system and embodied in the Dawes Act, was favored by liberal reformers at the time, but eventually proved detrimental to American Indians as they sold most of their land at low prices to white speculators.