Yes. It would not have carried conviction if it were issued during a string of Union defeats.
The most significant event was the Union victory at Antietam. That gave Lincoln the excuse he had been waiting for to issue the Emancipation Proclamation.
Yes. He'd been waiting all summer (1862) for a Northern victory that would enable him to make the announcement without making it sound like a desperate measure. A few days after the unexpected Northern vistory at Antietam, he issued the Proclamation, to be effective from January 1st 1863.
Until Antietam everyone thought that the North might actually loose the war. Antietam was just the victory Lincoln had been waiting for allowing him to issue the Emancipation Proclamation.
He was simplywaiting for a Union victory. It happened at Antietam (Sharpsburg).
Lincoln would have announced his Emancipation Proclamation a few weeks earlier than he did. (He had simply been waiting for a Northern victory, so that he would not look as though he was making a desperate gesture.)
It was Northern win that Lincoln had been waiting for, so that he could issue the Emancipation Proclamation - turning the war into a crusade against slavery, so that Britain and France could not aid the Confederates without looking pro-slavery themselves.
Antietam was the first major battle fought on Union soil that forced General Lees army to retreat back south of the Potomac River. It was the bloodiest one battle in American history. It gave President Lincoln the confidence to announce the Emancipation Proclamation.
Because he'd been waiting for a Union win, so he could issue the Proclamation without making it sound like a desperate measure. Through the summer, Lee's string of victories had led the British to believe that the Confederates would win, and they were planning to grant recognition. Lincoln decided to present the war to the outside world as a crusade against the evils of slavery, to shame the British into dropping their plans. This was what the Proclamation was really about. When the (unexpected, largely accidental) Union victory happened at Antietam in September, he issued the Proclamation within days.
Because they were losing all their battles in Virginia, and it would have looked like a desperate measure.
Lincoln first discussed the idea with his cabinet in July 1862, but the cabinet's advice and Lincoln's own feeling was that he should wait to announce the Proclamation until after a Union battlefield victory, so it would not appear to be a last desperate shriek from a losing nation. Waiting for a victory took a long time, before finally the Union army delivered what looked to be close enough at Antietam, which was really a tactical draw, but the Confederates pulled back afterward. Lincoln announced the preliminary Proclamation five days after the battle, on September 22, 1862. The Proclamation did not take effect until January 1, 1863.
freeing the slaves
It affected the war by giving the North an strategic advantage. The Battle of Antietam was the bloodiest day of the Civil War (September 17, 1862). Because the Union Army considered the battle a victory, President Abraham Lincoln issued the preliminary Emancipation Proclamation. He had been waiting for a Northern victory as a good time for the proclamation. About 2,000 Northerners and 2,700 Southerners were killed in this battle. Approximately 19,000 men from both sides were wounded, and about 3,000 of them would later die from these injuries.