How and why did the North and the South drift apart in the years between 1789 and 1850?

At the
time the Constitutional settlement was finalized in 1789 and the new federal government went
into action, the new country's unity was still something largely theoretical. Though
independence had been a fact for six years, the land west of the Alleghenies was still partly
occupied by the British, who had continued to hold their forts in the Northwest territory. There
was no plan in place regarding the Native Americans and the potential conflicts that would
continue to erupt as the settlers moved west and attempted to claim more and more land. There
was also a consciousness, on both sides of the Mason-Dixon line, that the slavery issue had been
shelved only temporarily, and that disagreements over it had been relegated to the background in
the interests of a common cause, first in 1776 in the effort to break away from the Crown, and
then in 1789 in the attempt to form the "more perfect union" that a majority of
Americans agreed was necessary.

Eventually slavery became the
principal...