Why was the congressional reconstruction unsuccessful and successful?

The southern(who were previously Confederate) states all wrote new Constitutions and swore loyalty to the Union by 1877. Also, the 13th amendment(which states no slavery nor involuntary servitude is allowed unless punishment... in u.s.), 14th amendment(forbids states to restrict simple rights of citizens etc,), and 15th amendment(citizens in U.S. cannot be denied due to race, color, etc. to vote) were acknowledged and remained after the reconstruction. Former slaves also had a new life ahead of them: they could now be educated, choose who they wanted to marry, and choose jobs. Unfortunately, the reconstruction didn't heal African American/ white man wounds; and even though there were laws for equality, for many upcoming years, many black people still had many problems with white people who still believed they were somehow superior.