How did lincolns and the unions attitude toward african americans change as the civil war progressed

Prior to the Civil War, Lincoln in the union did not object to slavery. Their objection was to the separation of the union, and was willing to keep slaves as slaves or free them if that meant that in the end, the union will remain unified. But as the Civil War progress, Lincoln and the union began to acknowledge that slavery should be abolished, and that slaves should be free. This is when Lincoln finally took a position of opposition to slavery which led to his drafting of the Emancipation Proclamation.