also dependent upon the existence of slavery in the South, given the critical importance of the cotton trade and the tariffs thereon, to the whole country.

Slaves, as property (to use your words, "as callous as that sounds"), represented the majority of the capital of the southern states and a sizable chunk of the capital of the entire country. And until the abolitionists came along, the entire country was complicit in the arrangement.

And before the Revolution (and in 1860 the post-Revolutionary period was significantly shorter in duration than the Colonial period, even including the sixteen years between the surrender at Yorktown and the ratification of the current Constitution, during which there really was no "United States of America.") of course slavery was an ENGLISH institution, as smug as they can now be about the racial morals of the American South, which THEY instilled.