What does it mean when w.e.b. du bois says that slavery went free stood a brief moment in the sun then moved back towards slavery?

Du Bois is referring to the period of Reconstruction after the Civil War when African Americans experienced some improvements in their rights and freedoms, only to see these gains eroded by the rise of Jim Crow laws and systemic racism. He is illustrating the cyclical nature of progress and setbacks in the struggle for racial equality in America.