Sioux or Dakota Indians, a North American Indian tribe, once spread over the territory lying between Lake Winnipeg (N.) and the Arkansas River (S.), but now confined chiefly to South Dakota and Nebraska. Failure on the part of the United States Government to observe certain treaty conditions led to a great uprising of the Sioux in 1862, which was only put down at a great cost of blood and treasure; conflicts also took place in 1876 and 1890, the Indians finding in their chief, Sitting Bull, a determined and skilful leader.