Reconstruction was, by most metrics and standards, a failure - at least, or especially, in the South.
To understand Reconstruction more thoroughly, you must understand the stated goals of Reconstruction policies ("de facto") vs. the actual enforcement (or lack thereof) of these new laws. You must also understand the depths of resentment and humiliation in the South. They had failed miserably in their quest for separatist glory; their land was in ruins; the most profitable basis of their agricultural economy was now illegal.
In retaliation for their loss, Southern whites took their frustrations out on the many newly free Black citizens of the South. If they could not have their own country, many Southern whites reasoned, they could still refuse to follow rules. When it came to the presence of Black people, Southerners found an easy scapegoat. They blamed Black people for their failure in the war, and generations-old racist ideologies came to a devastating head. From this chaos rose the KKK, patently unfair and unconstitutional laws restricting the rights of Black citizens, and a culture of white terrorism and violence that plagued the region.
The federal government, now focused on expansion and other more "pressing" national concerns, turned a blind eye, and the situation grew worse.