When Abraham Lincoln was elect in 1860 the southern states raged. Differences between North and South were bigger with that event, because Republicans had a anti-slavery policy.
The main Lincoln's purpose was to unify North and South in a strong Nation, powerful and independent. But, they saw that this goal was impossible to achieve if they don't finished slavery. With that abolishment, North and South had no longer differences.
The change was made by Abraham Lincoln because he saw the way slaves were treated by the south and which created a further reason for the union in the war
