Gettysburg was the Army of the Potomac's only great victory on the battlefield. Antietam, certainly a strategic victory, showed Robert E. Lee's unstoppable killing machine was indeed stoppable. And the Army of the Potomac did eventually force Lee's Army of Northern Virginia from its impregnable Petersburg trenches. But Lee's surrender at Appomattox Courthouse finally came when the Rebel army was so weakened that surrender was almost a foregone conclusion. Such Union victories as the ones at Sayler's Creek and Five Forks in the final weeks befo ....