>> with the emancipation proclamation hanging in the balance, george mcclellan's union army clashes with robert e. lee's confederate force in the battle of antietam. >> the second phase of the battle of antietam, this massive union attack right at the heart of the southern lines. and that's where the bloody lane occurs, when you've got this sunken road that's absolutely filled with casualties and running with blood. >> after hours of savage fighting, the union forces finally break through the center of the confederate line. mcclellan now has a chance to claim victory. all he has to do is send in his 20,000 reserve troops. >> we have them by the throat, general. [ gunfire ] we could send in the reserve and