The Wounded Knee Massacre was the culmination of decades of U.S. expansion, the violation of treaties, and the forced assimilation of Native Americans. In 1890 the Lakota people were struggling with hunger and the reduction of their reservation. Some of them turned to the Ghost Dance religion, which promised a return to their traditional lands and way of life. The Ghost Dance movement alarmed some U.S. officials, who saw it as a militant movement. The death of the Lakota leader Sitting Bull further heightened tensions on the Plains.