During the four years of the American Civil War, over 400,000 soldiers -- one in every seven who served in the Union and Confederate armies -- became prisoners of war. In northern and southern prisons alike, inmates suffered horrific treatment. Even healthy young soldiers often sickened and died within weeks of entering the stockades. In all, nearly 56,000 prisoners succumbed to overcrowding, exposure, poor sanitation, inadequate medical care, and...