The Slaughterhouse Cases were a series of Supreme Court decisions in 1873 that addressed the rights of African Americans and the limits of state power under the 14th Amendment. These cases are significant because they helped to define the scope of the privileges or immunities clause, ultimately ruling that it did not protect the rights of individual citizens from infringement by the states. This decision weakened federal protections for African Americans during the Reconstruction era and marked a shift towards states' rights, impacting the overall progress of civil rights at that time.