The main conflict fought between the North and South regions of the United States was the Civil War, primarily rooted in issues of slavery and states' rights. Starting in 1861 and lasting until 1865, the war pitted the Union (North) against the Confederacy (South) after several Southern states seceded from the Union. The conflict was characterized by significant battles and immense casualties, ultimately leading to the abolition of slavery through the 13th Amendment. The Civil War fundamentally reshaped the national landscape, determining the future of federal authority and civil rights in the United States.