The American Civil War was a conflict fought in the United States from 1861 to 1865. It primarily arose from tensions between the Northern states, known as the Union, and the Southern states, known as the Confederacy. Key issues included slavery, states' rights, and economic differences. The war began when Confederate forces attacked Fort Sumter in South Carolina. Major battles included Gettysburg and Antietam, leading to significant casualties on both sides. The war ended with the surrender of Confederate General Robert E. Lee at Appomattox Court House in 1865, ultimately resulting in the preservation of the Union and the abolition of slavery.