The outcome of the Civil War on the question of states' rights was a significant shift toward federal authority. Before the war, many Southern states championed states' rights, arguing that they could nullify federal laws. However, the Union victory reinforced the principle that the federal government held ultimate authority over states. Post-war amendments, particularly the 13th, 14th, and 15th Amendments, expanded federal power to protect the rights of newly freed slaves. This marked a new chapter in American federalism, emphasizing national unity over state sovereignty.