7 November 1837: A pro-slavery mob attacking the offices of the Alton Observer, killing the anti-slavery editor and proprietor, Elijah Lovejoy. (Photo by Hulton Archive/Getty Images)

African-Americans take away the dead and wounded after an attack by white supremacists in Louisiana, 1873. (Photo by Three Lions/Hulton Archive/Getty Images)

A group of men and women, presumably slaves, grind sugar with the help of mules and a simple machine on a farm, Georgia, mid 19th Century. A child sits atop on the fulcrum of the machine. (Photo by L.J. Schira/Hulton Archive/Getty Images)

A group of men and boys, presumably slaves, sit on and around a pile of barrels on a pier or dock, Jacksonville, Florida, mid 19th Century. (Photo by C. Seaver Jr./Hulton Archive/Getty Images)

circa 1865: Harriet Beecher Stowe, American anti-slavery author of, amongst other books, 'Uncle Tom's Cabin'. She is with a group of anti-slavery workers. (Photo by Hulton Archive/Getty Images)

Former slaves celebrate Emancipation Day in Charleston, South Carolina, a year after the end of the American Civil War, 1st August 1866. (Photo by Three Lions/Hulton Archive/Getty Images)