If the Confederacy had been a separate nation, it would have ranked as the fourth richest in the world at the start of the Civil War. The slave economy had been very good to American prosperity. By the start of the war, the South was producing 75 percent of the world’s cotton and creating more millionaires per capita in the Mississippi River valley than anywhere in the nation. Enslaved workers represented Southern planters’ most significant investment—and the bulk of their wealth.