The states needed to reconstruct their constitutions in a way that would grant freedom and rights to black persons who had been under slavery and now were to be considered citizens. There was much difficulty over this adjustment.
There also needed to be reconstruction of the land devastated by war and of the economy, also devastated by the war and now operating in a new way without the use of slave labor. Transitioning to a new style of economy was difficult.
Also in regard to economic issues, banking had been devastated in the South. By the end of the war, Confederate currency had become essentially worthless. Their whole system of finances needed to be reconstructed.