Sitting Bull did not agree to the treaty. He told the Jesuit missionary, Pierre Jean De Smet, who sought him out on behalf of the government: "I wish all to know that I do not propose to sell any part of my country." He continued his hit-and-run attacks on forts in the upper Missouri area throughout the late 1860s and early 1870s. The events of 1866–1868 mark a historically debated period of Sitting Bull's life. According to historian Stanley Vestal, who conducted interviews with surviving Hunkpapa in 1930, Sitting Bull was made "Supreme Chief of the whole Sioux Nation" at this time.
Sitting Bull natives joined him for safety in numbers. His leadership had attracted warriors and families, creating an extensive village estimated at more than 10,000 people. Lt. Col. Custer came across this large camp on June 25, 1876. Sitting Bull did not take a direct military role in the ensuing battle; instead he acted as a spiritual leader. A week prior to the attack, he had performed the Sun Dance, in which he fasted and sacrificed over 100 pieces of flesh from his arms. Custer's 7th Cavalry advance party attacked Cheyenne and Lakota tribes at their camp on the Little Big Horn