The major conflict fought over slavery in the United States was the American Civil War, which occurred from 1861 to 1865. The war arose mainly due to the contentious issues surrounding slavery, particularly in relation to its expansion into new territories and states. The Southern states, which depended on slave labor for their agricultural economy, seceded from the Union and formed the Confederacy, while the Northern states, known as the Union, sought to preserve the nation and ultimately abolish slavery. The conflict resulted in significant loss of life and ultimately led to the emancipation of enslaved people, reshaping the future of the United States.