The conflict primarily fought over the issue of slavery in the United States was the American Civil War, which lasted from 1861 to 1865. The war erupted between the northern states (the Union) and the southern states (the Confederacy) over various issues, including states' rights and, fundamentally, the institution of slavery. Southern states sought to preserve slavery as integral to their agricultural economy, while Northern states increasingly opposed it. The Civil War resulted in significant casualties, profound social changes, and ultimately led to the abolition of slavery through the 13th Amendment in 1865.