The major conflict that took place between 1861 and 1865 in the United States is the Civil War. This war was primarily fought over the issues of slavery, states' rights, and economic differences between the Northern states (Union) and the Southern states (Confederacy). The conflict resulted in significant battles, including Gettysburg and Antietam, and ended with the surrender of General Robert E. Lee in 1865. The Civil War led to profound social, political, and economic changes, including the abolition of slavery through the 13th Amendment. Its legacy continues to shape American society and race relations to this day.