That is flatly false and any general history of the war will tell you that it is false.
Slavery was a state institution clearly protected in the Constitution. President Lincoln had NO power to affect it in the normal course of administering the government. He had revoked emancipation initiatives by Generals Hunter and Butler early in the war.
He based the EP on his constitutional powers as commander in chief of the armed forces.
He wrote a famous letter to James Conkling for public distribution:
"But, to be plain, you are dissatisfied with me about the negro. Quite likely there is a difference of opinion between you and myself upon that subject. I certainly wish that all men could be free, while I suppose you do not. Yet I have neither adopted nor proposed any measure, which is not consistent with even your view, provided you are for the Union-- I suggested compensated emancipation; to which you replied you wished not to be taxed to buy negroes. But I had not asked you to be taxed to buy negroes, except in such way, as to save you from greater taxation to save the Union exclusively by other means--
You dislike the emancipation proclamation; and, perhaps would have it retracted-- You say it is unconstitutional-- I think differently. I think the constitution invests it's commander-in-chief, with the law of war in time of war-- The most that can be said, if so much, is that slaves are property. Is there -- has there ever been -- any question that by the law of war, property, both of enemies and friends, may be taken when needed? And is it not needed whenever taking it, helps us, or hurts the enemy?
Armies, the world over, destroy enemie's property when they can not use it; and even destroy their own to keep it from the enemy-- Civilized beligerents do all in their power to help themselves, or hurt the enemy, except a few things regarded as barbarous or cruel-- Among the exceptions are the massacres of vanquished foes, and non-combattants, male and female.
But the proclamation, as law, either is valid, or is not valid. If it is not valid, it needs no retraction. If it is valid, it can not be retracted, any more than you can bring the dead can be brought to life. Some of you profess to think it's retraction would operate favorably for the Union. Why better after the retraction, than before the issue? There was more than a year and a half of trial to suppress the rebellion before the proclamation issued, the last one hundred days of which passed under an explicit notice that it was coming, unless averted by those in revolt, returning to their allegiance. The war has certainly progressed as favorably for us, since it's the issue of the proclamation as before.
You say you will not fight to free negroes. Some of them seem willing to fight for you; but, no matter. Fight you, then exclusively to save the Union. I issued the proclamation on purpose to aid you in saving the Union. Whenever you shall have conquered all resistence to the Union, if I shall urge you to continue fighting, it will be an apt time then for you to declare you will not fight to free negroes.
I thought that that in your struggle for the Union, to whatever extent the negroes should cease helping the enemy, to that extent it weakened the enemy in his resistence to you-- Do you think differently? I thought that whatever negroes can be got to do as soldiers leaves just so much less for white soldiers to do, in saving the Union. Does it appear otherwise to you? But negroes, like other people act upon motives-- Why should they do any thing for us, if we will do nothing for them? If they stake their lives for us, they must be prompted by the strongest motive -- even the promise of freedom. And the promise being made, must be kept."
8/23/63
You obviously don't know the history.
President Lincoln well knew that the EP only had force as a war measure. That is why he was a strong advocate of the 13th amendment.
Walt