“Could very well have ended the war had the South freed their slaves...”
This raises the question: If the North wanted to free the slaves, why not introduce and pass a constitutional amendment in 1850, or 1860, or 1861 to abolish slavery? Then the war and all the killings and all the destruction and all the hard feelings could have just been skipped.
After the war, Jefferson Davis said they should have just used Article V and prevented the bloodshed.
There were fifteen slave states. If all had opposed the amendment it would have taken 46 states to ratify it. Do the math.