Civil War and Reconstruction. The war shifts from a struggle for union to a battle over slavery. Blacks, such as South Carolina slave and future congressman Robert Smalls, contribute to the war effort and experience gains and losses from Reconstruction. The 13th, 14th, and 15th amendments abolish slavery and guarantee black civil rights, and the Freedmen's Bureau offers aid to former slaves throughout the 1870s. But militant groups such as the Ku Klux Klan threaten the future of racial equality, and segregation laws begin appearing across the country. Slavery's eradication does not end black oppression.