In 1877, some of the Lakota bands signed a treaty that ceded the Black Hills to the United States; however, the nature of this treaty and its passage were controversial. The number of Lakota leaders who actually backed the treaty is highly disputed. Low-intensity conflicts continued in the Black Hills. Fourteen years later, Sitting Bull was killed at Standing Rock reservation on December 15, 1890. The U.S. Army attacked Spotted Elk (aka Bigfoot), Mnicoujou band of Lakota at the Wounded Knee Massacre on December 29, 1890, at Pine Ridge.