The major conflict fought between the North and South in the United States was the Civil War, which lasted from 1861 to 1865. The underlying causes of the war included regional differences over slavery, economic competition, and states' rights. The election of Abraham Lincoln, who opposed the expansion of slavery, prompted several Southern states to secede from the Union and form the Confederacy. The war featured significant battles such as Gettysburg and Antietam and concluded with the defeat of the Confederacy. The Civil War led to the abolition of slavery and fundamentally transformed American society and governance.