I believe it came from above because President Lincoln was the one who changed the war's purpose. At first, he declared that the purpose was to save the Union from perishing, but later changed it to earning the freedom of enslaves Americans. In the Gettysburg Address he declared, "That this nation under God shall have a new birth of freedom, and that the government of the people, by the people, shall not perish from the earth. This was the first time Lincoln acknowledged abolition movement influencing the war. Even though he was afraid to lose the loyalty of the border states to the Confederacy he changed the goal of the war to benefit his citizens. If he never did this the enslaved Americans would have no supporters from above and no one would take them seriously.
President Lincoln giving the enslaved Americans their freedom
Although President Lincoln made the first, official move his actions were influenced greatly by the current enslaved Americans. The slaves would walk off the plantations they were working at to follow the Union army. While following them they would constantly pester the army. As a result, the army would go to their superiors to ask what to do about the slaves that were following them. The superiors then turned to the government because they didn't know what to do as well. These chain reactions forced Lincoln and the government to do something to stop the constant pestering the Union army was enduring.
Also, I believe that the enslaved Americans had a lot to do with their new found freedom causing freedom from below. The way they got their freedom was to take action by marching into the city and overrun it. They overran it by taking the things that appeal to them and living in empty buildings that they found. Their actions ensured that their freedom came from below because the whole thing started with the slave's actions that are forcing higher powers, such as the president, to react to the scenes they are causing.