It was after the rather lucky Union win at Antietam (Sharpsburg) in September 1862, which gave Lincoln the chance to issue the Proclamation without making it sound like a desperate measure.
The Battle of Antietam near Sharpsburg, Maryland ended Lee's first attempt to enter the North. It was fought on 17 September 1862 and the Emancipation Proclomation was issued on 22 September 1862...