yes it was an advantage because Lincoln only freed slaves in rebellious states (the south). Since the north had not had good luck on the battlefield up to that point Lincoln made a statement and said if God would grant the north victory he would free the slaves. shortly after that the north had there first victory at Antietam. on Jan 1st 1863 Lincoln officially freed the slaves. But many slaves that where freed had no where to go, so Frederick Douglas proposed an idea to Lincoln that the former slaves take up arms and fight, which they did. the most famous all black regiment being the 54th Massachusetts.