A hundred and fifty years ago, the Osage Nation bought a stretch of prairie the size of Delaware, in what's now Oklahoma. The Osage owned the land and everything beneath it. Today, much of present-day Osage County has left Osage hands. In some cases, appropriation was swift and brutal: Dozens of Osages were murdered for their share of lucrative mineral rights to this oil-rich land, a period often referred to as the Reign of Terror. But other transfers of wealth played out more subtly—dollar by dollar and acre by acre, over decades—helped along by policies created by the US...