Which event effectively ended the American Civil War?

The event that effectively ended the American Civil War occurred when General Robert E. Lee surrendered to General Ulysses S. Grant at Appomattox Court House on April 9, 1865. This surrender marked the conclusion of major Confederate military operations, signaling the collapse of the Confederate resistance. The surrender was significant not just for its immediate military implications but also for its symbolic value, representing a turning point in the long and bloody conflict. Following Lee's surrender, many other Confederate forces also surrendered, leading to the eventual conclusion of the war.

The other options do not serve as endpoints for the war. The Military Reconstruction Act was a legislative measure aimed at the reconstruction of the South but came after the war had already concluded. The Emancipation Proclamation, issued in 1863, declared the freedom of slaves in Confederate states, but it did not end the war; rather, it redefined the Union's war aims. The Battle of Gettysburg, fought in 1863, was a significant turning point in the Civil War, marking a major defeat for the Confederacy, but it did not end the conflict itself.