The answer is The U.S. Army. In 1890 the U.S. government was worried about increasing influence of the Ghost dance spiritual movement. Believing that Sitting Bull a Sioux leader was a ghost dancer he was arrested but killed in the processes. On December 29, the U.S. Army’s 7th cavalry surrounded a band of Ghost Dancers under the Sioux Chief Big Foot near Wounded Knee Creek and demanded they surrender their weapons. It’s uncertain who fired first but weapons were fired resulting at least 150 Indians being killed. This battle is known as the Massacre at Wounded Knee.