What Civil War battle led President Lincoln to issue the Emancipation Proclamation to free the slaves in the Confederate states?

Answer:
Antietam/Sharpsburg, Sept. 1862.

If he had issued the Proclamation any earlier, it would have looked like a desperate measure, following a string of Confederate victories in the summer.
First answer by Jonathan Begg. Last edit by Jonathan Begg. Contributor trust: 152 [recommend contributor recommended]. Question popularity: 1 [recommend question].