The 1870 Drum Creek Treaty forced the Osage off their land to Oklahoma Indian Territory. The Osage became the only tribe to purchase their own reservation. They chose land "the white man would never want or be able to use." They obtained mineral rights to this property, and in the 1920s when oil was discovered, the Osage became the richest people per capita in the world. This extreme wealth led to the "Reign of Terror," where hundreds of Osages were murdered to obtain their inheritance headrights. The newly formed FBI took over the investigation of the murders, but most of the death cases remain unsolved.