The initial few years of Reconstruction were ones of black power and freedom. Recently freed black people, specifically on the coast of Georgia and the Carolinas, were able to claim land from former plantation owners who fled the south after the Civil War ended. For the first time, formerly enslaved black people were able to freely live on the land that they had been forced to toil on for their whole lives. In government, an interracial alliance of blacks and white was beginning to form. However, racist violence from vigilante groups, such as the KKK and racist political parties and individuals, resulted in the overturning of the initial victories of Reconstruction.
In the south, incredibly violent and often murderous racist mobs attacked newly freed black people and their white allies. The South became overrun with these mobs, and there were not enough Union troops still stationed to address the violence. Meanwhile, racist Southern political groups began creating and enforcing "Black Code" laws that rolled back all successes of Reconstruction. When Andrew Johnson became president, he aided Southern racists in their goals of crushing Reconstruction. Johnson ordered the abandoned land to be given back to the white plantation owners and supported the creation of the Black Codes.
These codes that became known as the Jim Crow laws excluded black people from the political process, made owning land extremely difficult, gave rise to mass incarceration of black people, enforced segregation, and overturned the formation of the interracial government. With the Jim Crow laws in effect, white racists were able to terrorize black people and their white allies with little to no consequence.
Reconstruction failed to bring equality to the freed slaves because it would have been very hard to bring them equality even if the government had had more power and will than it actually did.
Right after the war, the freed slaves were inferior to whites socially, politically, and economically. It would have been exceedingly hard for the government to have fixed all of these things. There was no way that governmental fiats could have made blacks and whites equal on a social basis. They might possibly have been made equal in the eyes of the law, but whites were simply not going to see blacks as their equals. It would have been very hard to make the African Americans economically equal to whites. They lacked education. They lacked land to farm on and it would be legally and politically very difficult in our system to take land away from the plantation owners and give it to the slaves. Political equality was easier to give since it involved only allowing African Americans to vote.
Even if these things could have been achieved, they would have taken effort on the part of the government. It took a military occupation of the South to even get blacks to be granted political rights. The North was not willing to continue to occupy the South just to accomplish this. Because of this lack of will, Reconstruction ended and blacks were still not equal to whites on any level.