The Black Hills, called Paha Sapa by the Lakota and held as the sacred center of the Lakota universe, were guaranteed to the Great Sioux Reservation by the Fort Laramie Treaty of 1868, a formal agreement the United States itself signed. The discovery of gold there in 1874 broke that guarantee within a few years, as prospectors moved in and the government seized the Black Hills outright rather than enforce the treaty against them. The Supreme Court's own 1980 ruling in United States versus Sioux Nation of Indians found the seizure unconstitutional and ordered compensation, a judgment the Lakota nations have consistently refused to accept, holding instead that the land itself, not a monetary settlement for it, is what the treaty actually promised, so the compensation has sat uncollected and accruing interest for decades rather than being taken.
The Ghost Dance movement of the late 1880s, a Native religious revival built around visions of ancestors returning and settler expansion being undone, spread to the Lakota at a moment of already acute crisis over the Black Hills seizure and the collapse of the buffalo economy, and government officials read the movement's spread as a prelude to armed uprising. That fear led directly to the 1890 massacre at Wounded Knee on the Pine Ridge Reservation, where the United States Army killed several hundred Lakota men, women and children, an event that ended large scale armed Lakota resistance and remains, in Lakota memory and in the scholarship built on Ghost Dance sources, a site of mourning and pilgrimage rather than a closed historical episode.