4) the removal of federal troops from the South
Troops were removed from the South when Reconstruction ended officially in 1878. Prior to that the South was under the leadership of Radical Republicans who ensured Southerners followed new amendments and laws to create an slave-free society.
Following the end of Reconstruction, Southerners began a series of laws referred to as the Jim Crow laws. These laws created a system of segregation in the South. In addition, laws were created to limit blacks' ability to vote. Literacy tests and poll taxes were put into place which virtually took away a black man's right to vote. This system of legal discrimination and segregation continued for nearly 100 years in the South.