The American Civil War, which lasted from 1861 to 1865, resulted in a significant shift in federal-state relations, fundamentally altering the nature of the United States government. The Union's victory ensured the preservation of the nation and led to the abolition of slavery through the 13th Amendment. It also strengthened the power of the federal government over the states, as questions regarding states’ rights were resolved in favor of federal authority. This shift facilitated the federal government’s active role in social and economic issues, laying the groundwork for future advancements in civil rights and federal intervention in state affairs, thus shaping the course of American governance.