 The Lower Brule Sioux Tribe is a sovereign nation defined by its government-to-government relationship with the United States.As part of the Great Sioux Nation, the Tribe signed treaties in 1824, 1851, 1865 and 1868 with the federal government that constitute the legal documents establishing boundaries and recognizing the rights of sovereign tribal governments.The Tribe was chartered under the Indian Reorganization Act of June 18, 1934.