Factual error: The movie depicts Col. Nelson Miles at the signing of the Fort Laramie Treaty which was signed April 29, 1868. Col. Miles is shown wearing a Civil War Medal and an Indian Wars Medal. The first Civil War Campaign Medal was issued in May 1909 and the blue and gray ribbon shown in the film was not in use until August 1913. The first Indian Wars Medal was issued July 1908. The ribbon shown in the film with two dark bands was not in use until 1917. Obviously, Col. Miles could not wear two metals that have not been created yet.
Factual error: The movie depicts Wes Studi, who is playing the Paiute medicine man "Wovoka," as coming to the Sioux reservation and delivering his vision. Wovoka (aka Jack Wilson) was from Schurz, Nevada 1250 miles away from the Pine Ridge Reservation in South Dakota. He never travelled to South Dakota. What really happened was tribal parties (at great personal risk) travelled to Nevada to get the message and brought it back to the Sioux people. Of course, this message was "modified" somewhat to better fit Lakota culture.
Factual error: In the hospital scene that follows the result of the arrest of Sitting Bull, and of his death at the hands of the tribal police, one woman tells Adam Beach what happened. Adam then goes over to another patient who tells of what happened at Wounded Knee. There is 293 miles distance between where Sitting Bull was killed at the Standing Rock Reservation and Wounded Knee, which is on the Pine Ridge Reservation. The wounded could not have possibly travelled in the dead of winter to get to a hospital in 1890 South Dakota.