To what extent was the Emancipation Proclamation purely military motivated?
Most people assume, and have been taught by popular culture, that when Abraham Lincoln issued the executive order known as the Emancipation Proclamation that he "freed the slaves." This is not actually true. The Emancipation Proclamation was merely a tactically advantageous military action designed to hinder the south's steady gains up until that point in the Civil War.
The Emancipation Proclamation was militarily driven in that it only applied to the slaves that were in states that were in active rebellion; in other words, any of the southern slave holding states that had seceded from the Union. This action therefore applied to approximately 3 million of the 4 million slaves in the United States at the time with the intention of freeing these 3 million able-bodied persons to then fight the Confederacy in their own territory or to escape to the North and likewise take up arms against the south from there. This left just under 1 million slaves still in bondage in states that had not left the Union as President Lincoln's executive war powers only extended into enemy states. The remaining slaves would not be officially freed until the passing of the 13th, 14th, and 15th amendments after the end of the war.