Replaced by what? There were almost 4 million slaves.
The policy was falling out of favor, & the blacks that were there were free people who worked the land for part of the crops, and a sense for belonging. Was it right to own another person, NO it is not, and this way of living was coming to an end befoe the war had started. It was only the extermly large plantions had owned slaves, but that was costing more money to keep them there forcefully, but instead if the had wanted to stay that made the job easier. Why whip a person into submission, when you could entice them into staying by choice. They would produce much more in the way of crops, timber ect... by choice not by force.