David I am sure that you are aware that any political decision is made to gain the most political impact, and is not usually directed solely at a single purpose. The question is what was the total impact of the E.P.? And assigning the correct weight of history to each of those purposes. Such as, was it intended to cause the southern slaves to revolt? That is one of its claimed purposes also.
Keeping England out of the War, Keeping New England in the war. possibly inciting the southern slaves to revolt, were all definate political advantages for Lincoln. But actually freeing the slaves which he had the ability to lobby his Congrees to do, Lincoln did not do that. For if Lincoln had actually freed the slaves in the North he would have probably lost the support of the western and border states.
So he walked a very thin line of freeing the slaves that he could not free, and leaving as slaves those which he could have freed. I give you again the case of the admission of West Virginia to this union, as a SLAVE State, post E.P.