The conflict fought between the Northern and Southern states in the U.S. primarily over slavery is known as the American Civil War. Lasting from 1861 to 1865, this war arose from deep-seated issues surrounding slavery, states' rights, and economic differences. The Southern states seceded from the Union to form the Confederate States of America, primarily to preserve and expand the institution of slavery. In contrast, the Northern states, led by President Abraham Lincoln, fought to maintain the Union and ultimately to abolish slavery. The war resulted in significant loss of life and set the stage for the Reconstruction era and civil rights advancements.