"Our political problem now is “Can we, as a nation, continue together permanently—forever—half slave, and half free?" Abraham Lincoln, 1855
When Lincoln first asked this question, America was slowly coming to grips with the knowledge that as a nation it could not continue to exist, half-slave and half free. This was not only because slavery was immoral or unconstitutional... but on a purely practical level, slave states and free states had significantly different and incompatible interests.