After the war was over, Lincoln was murdered and the North's desire for revenge had never been stronger. Certainly, had Lincoln lived, he would have forced reforms in the South, but would have held back the strongest Northern extremists that wanted to treat the entire South like a conquered country and repopulate it with their own people.
Lincoln however, did not live to see his reconstruction plans through and it was left to Johnson to figure out exactly what the South was and wasn't with respect to its place in the country.
Was the South part of the United States again? Was it some sort of territory that the Federal government needed to oversee? If it was not immediately welcomed back into the Union, then what would the conditions be that would allow it back in? Should it pay reparations to what now is its own government?
The questions go on and on and are extremely complex.
Johnson was of the school of thought that the policy of the North should be one of forgiveness.
I should note that this was also Lincoln's policy, but where Johnson and Lincoln would seem to differ is that as soon as the South surrendered and its soldiers took a loyalty oath to the United States (southerners called this 'walking the dog') they were completely United States citizens again.
Johnson wanted southern states to rejoin the Union as fast as possible and pardoned high level members of the rebellion.
He said nothing when the same people that served as congress members of the confederacy eagerly rejoined the Congress of the United States and their own state's house of representatives. This begs the question of how things were any different after the Civil War politically between the North and South.
Although he outlawed slavery, he did nothing to prevent the 'black codes' from going into effect and stood by when virtually all southern states disenfranchised the recently freed blacks.
He did what he could to prevent the public works projects for teaching freed slaves business or trade skills and sent letters of support in favor of programs to send free blacks overseas or down to Mexico.
Johnson put the South in a strange position. Before and during the war, he was completely hated for his sympathies for the Union cause and his distrust of rebellion. After the war, he was loved for the way he tried to make everything the way it was before the war, minus slavery of course. Poor whites stepped into a world where they had somewhat more upward mobility since they no longer had to compete with no wage workers and the former slaves were largely excluded from political and economic life.
In short, Johnson made things as good as possible for white Southerners and made things as bad as possible for freed slaves.