What developments deepened the divisions between the north and the south

 The south had slaves and the north had abolitionists (people who did not like slavery). And as such the north started to protest the actions of the south. The north started to provide safe haven for run away slaves from the south, and this rather displeased the south. The south viewed this as a direct affront to their rights as U.S. citizens, claiming that the slaves were their property and the north is stealing it.