What were the reasons that the Battle of Antietam helped Lincoln decide to issue the preliminary Emancipation Proclamation?

The Battle of Antietam was the one of the Bloodiest one day battles of the war at that point that resulted in a decisive win for the Union. This big win gave the Union the knowledge that they could win aganist the confederacy which resulted in a gain of confidence for the Union. This win was a win in more ways than one, it was a win in the Eastern war front which had been a strong hold for the confederacy. Lincoln used the confidence of this win to issue the Emancipation Proclamation from a position of strength rather than need.

Explanation:

answer; ethnocentric;

stable food supply,social structure, government,religion,culture/art,technology and writing/language;