In your opinion, what was the most serious mistake of reconstruction?

Compromising with the old Southern aristocracy, allowing them to seize control and pass the Jim Crow legislation that largely negated emancipation of the slaves leaving them little more than poor, second class citizens for the next century. In the end the Civil War was not resolved until the Civil Rights Movement of the late 50s and early 60s succeeded in repealing these Jim Crow Laws that held the Black population down.