The problems facing the South were immense. Short of massive land confiscation, or the federal government buying up large amounts of land to redistribute to the freedmen, there was no way to set up all the former slaves with their own farms (their preference).
It was a principle of common law that ordinary citizens can't be punished for obeying the government actually in power (that dates back to the Wars of the Roses), so it would have been hard to justify seizing property from ordinary Southerners, not to mention the tremendous opposition and hatred that would have generated--a sure formula for guaranteeing that the Union never got back to normal.
Behind it all was racism, an unrecognized problem--both Northerners and Southerners had grown up with racial attitudes which precluded seeing blacks as equal to whites, and for the federal government to go to great lengths for the former slaves would be a losing political program for the Republicans in the North. In the period just after the war, several Northern states rejected giving black men the vote.
The Southern whites accepted the fact they had lost the war and that slavery was over, but as someone put it at the time, they felt that the black race as a whole belonged to the white race as a whole (instead of individual black people belonging to individual whites), and they wanted the free blacks to continue to work for the whites. That, in part, was what the Black Codes were all about.
Colonization in Africa was totally impractical. Very few black Americans wanted to leave. Lincoln experimented with colonization during the war (on an island off Haiti) and it was a disaster.
An excellent new book on the polarization that led to the war is Thomas Fleming's A Disease in the Public Mind: A New Understanding of Why We Fought the Civil War