It's kind of like we never satisfactorily resolved the end of slavery, we had to amend the Constitution in the 1960's because of states scamming African Americans of their right to vote because the post Civil War amendments did not outright prevent weasels from making it hard to vote for people of the wrong skin tone. We might have been further along now if Woodrow Wilson hadn't helped resurrect the KKK and started bringing racial discrimination and segregation into the federal government, the latter development took close to 50 years to roll back.
Arguably Lincoln, Johnson, and Grant were too kind to southern aristocrats. What they should have done, historic atrocities as a guide, is executed the entire aristocracy down to the children and divided up the land to the slaves. We'd certainly have been further along now had that happened.
But Grant threatened resignation if pardons were not granted to Lee and all who surrendered at Appomattox. These men were absolutely over the war, and as the papers of the day indicate, most people were too. There really was no meaningful demand for treason trials for the lead generals.
And the sadly, as the Civil War determined slavery was absolutely wrong, it began 100 years of institutionalized 2nd class citizenry based on skin color. The Civil War was not a successful egalitarian enterprise by any stretch of the imagination.