April 10, 1865: General Robert E. Lee surrendered the Army of Northern Virginia to General Ulysses S. Grant, effectively ending the Civil War.
Actually, General Lee surrendered the Army of Northern Virginia at Appomattox Courthouse, Virginia on Sunday, April 9th, 1865, not April 10th. This was not the end of the war as Lee only surrendered his immediate command, not the entire Confederate military. Having said that, it was the major Confederate army in the east and without it there was little hope of the Confederacy surviving. The last Confederate military department, the Trans-Mississippi Department was surrendered at Galveston, Texas on 02 June 1865 (negotiated at New Orleans 26 May, but not signed until 02 June by Lt. Gen. Edmund Kirby-Smith at Galveston).