This problem started when the nation was born, because the founding fathers passed on dealing with the Slavery Issue in order to bring about independence
The leaders of the country kept punting the problem down the field (much like they are doing today with the economy) and through a series of compromises it held until 1850 and California entered the union as a non slave state (which was against the compromise) that sent the ball rolling to and it's inevitable conclusion. Dissoultion.