What were the driving forces behind the abolition of slavery?
I think that a strong argument can be made to suggest that it was social forces that were behind the abolition of slavery. The justification of slavery in the South was heavily rooted in economic arguments and the Northern part of the United States was more concerned with economic industrialization in more parts. Slavery was not as looming of an economic concern as much as fortification of the Northern industry. Politically, few, if any forces, were able to muster the courage to be able to articulate an effective stand. If they were, such forces were met with equal ferocity by the Southern political forces that framed slavery as an issue of tradition and state rights.
It was in the social forces that did much to drive the cause of the abolition of slavery. Abolitionists such as the Grimke sisters, William Lloyd Garrison, and Frederick Douglass sought to give voice to the movement and helped to force the issue of the abolition of slavery in the national consciousness. Feeding off of the Second Great Awakening that advocated a more devout and spiritual embrace of Christianity, these thinkers were instrumental in generating social opposition to the institution of slavery.
Most notable of them was Harriet Beecher Stowe, who framed the issue of slavery in moral and religious terms through Uncle Tom's Cabin. When President Lincoln meets Stowe and refers to her as the "little lady who started the Civil War," it is a reflection of how social forces created the calls for abolitionist change and how social forces can shape history. Here again one sees social forces driving abolition. Individuals like Levi Coffin and Harriet Beecher Stowe took social words into social activism in providing shelter and passage to runaway slaves from the South to the North.