What was the legal assumption surrounding the treatment of the South after the Civil War?

The legal assumption regarding the treatment of the South after the Civil War was that secession was illegal. This perspective was rooted in the belief that the Union, as a continuous entity, was never truly broken by the Southern states' attempts to secede. The prevailing view among the federal government and President Abraham Lincoln was that since the Constitution did not provide for states to unilaterally withdraw from the Union, the Southern states that had seceded remained part of the United States, even if they were in rebellion.

This idea was reinforced by the outcomes of the war, which effectively served as a military confirmation of the idea that the Union must remain intact and that the actions of the secessionist states were unconstitutional. Thus, the post-war Reconstruction era focused on reintegrating these states into the Union while addressing the complexities surrounding their status and the rights of freed slaves.

The notion that secession was treated as illegal significantly influenced the Reconstruction policies, as it meant that the federal government aimed not just to punish the former Confederate states, but also to restore them to their rightful place in the Union, facilitating their reintegration under new terms that would safeguard civil rights and redefine their role within the national framework.