White supremacy was dominant in the United States both before and after the American Civil War, and it persisted for decades after the Reconstruction Era.[29] Prior to the Civil War, many wealthy white Americans owned slaves; they tried to justify their economic exploitation of black people by creating a "scientific" theory of white superiority and black inferiority.[30] One such slave owner, future president Thomas Jefferson, wrote in 1785 that blacks were "inferior to the whites in the endowments of body and mind."[31] In the antebellum South, four million slaves were denied freedom.[32] The outbreak of the Civil War saw the desire to uphold white supremacy being cited as a cause for state secession[33] and the formation of the Confederate States of America.[34] In an 1890 editorial about Native Americans and the American Indian Wars, author L. Frank Baum wrote: "The Whites, by law of conquest, by justice of civilization, are masters of the American continent, and the best safety of the frontier settlements will be secured by the total annihilation of the few remaining Indians."[35]