Great Sioux reservation

The Great Sioux Reservation was the original area encompassing what are today the various Indian reservations in South Dakota and Nebraska.

The reservation was established in the Fort Laramie Treaty of 1868, and included all of present-day western South Dakota (commonly known as "West River" South Dakota) and modern Boyd County, Nebraska. This area was established by the United States as a reservation for the Teton Sioux, also known as the Lakota: the seven western bands of the "Seven Council Fires" (the Great Sioux Nation).

In addition to the reservation dedicated to the Lakota, the Sioux reserved the right to hunt and travel in "unceded" territory in much of Wyoming and in the Sandhills and Panhandle of modern Nebraska. Because each band had its own territory, the US established several agencies through the Bureau of Indian Affairs to regulate the Lakota in this vast area.

The United States used the Missouri River to form the eastern boundary of the Reservation, but some of the land within this area had already assigned to other tribes, such as the Ponca. The Lakota Nation considered the West River area central to their territory, as it had been since their discovery of the Paha Sapa (Black Hills) in 1765, and their domination of the area after they conquered and pushed out the Cheyenne in 1776.

Custer's 1874 Black Hills Expedition from Fort Abraham Lincoln (near Bismarck, Dakota Territory) to the Black Hills or Paha Sapa discovered gold. The public announcement brought miners and open conflict with the Lakota. The US Army defeated the Lakota in the Black Hills War. By a new treaty of 1877, the US took a strip of land along the western border of Dakota Territory 50 miles (80 km) wide, plus all land west of the Cheyenne and Belle Fourche Rivers, including all of the Black Hills in modern South Dakota.

...
Wikipedia