During the Reconstruction US Congress passed a series of laws and amendments that aimed to reach equality for African Americans and ex-slaves, for example, the 13th, 14th and 15th Amendments and The Freedmen’s Bureau Act of 1866, the Civil Rights Act of 1866, the Civil Rights Act of 1870, the Civil Rights Act of 1871, the Civil Rights At of 1875.
Despite that, the US Supreme Court decided in a series of landmark cases contrary to those rules, making possible for the several Southern States to create segregation and establish Black Codes.
In United States v. Cruikshank the US Supreme Court decided that the Bill of Rights did not apply to private acts and to state governments, which meant that the Southern States did not need to protect the basic rights of African Americans.
In the Civil Rights Cases, the US Supreme Court ruled that the 13th and 14th Amendments did not outlaw racial discrimination by private individuals, which meant that commerces could discriminate African Americans if they wanted to.
In United States v. Harris the Supreme Court decided that it was unconstitutional for the federal government to penalize crimes as assault and murder, this case affected African Americans because it was known as the Ku Klux Case.