The correct significance of the Battle of Antietam relative to the Emancipation Proclamation is:
The Union victory gave Lincoln the strength and support needed for the issuance of the proclamation.
The Battle of Antietam, fought on September 17, 1862, was the bloodiest single-day battle in American history and was considered a strategic victory for the Union. The outcome provided President Abraham Lincoln with the political momentum he needed to issue the preliminary Emancipation Proclamation, which announced his intent to free the enslaved people in the Confederate states.