The significant document that effectively ended the American Civil War was the Treaty of Appomattox Court House, signed on April 9, 1865. This historic agreement marked the surrender of Confederate General Robert E. Lee to Union General Ulysses S. Grant, symbolizing the collapse of the Confederate rebellion. While not a formal treaty, the terms of surrender were significant in determining the terms of reintegration for the Southern states. Ultimately, this event paved the way for the Reconstruction era, during which the country sought to heal the divides caused by war and address the complexities of rebuilding the nation.