I'm certainly no expert on this question, and I defer to those who have more authoritative knowledge, but the evidence I've seen is that tariffs were not the major factor in leading to secession and war. Indeed, according to one source, there was no effort to get Buchanan to commit himself to vetoing the tariff, and Robert Toombs voted for the tariff, either because it wasn't regarded as harmful, or because it could be used as a pretext for secession and a provocation to Britain to condemn the unionists. Had all Southern Senators remained in Washington, the measure probably could have been tabled, since the Senate rules of the day required a 2/3 vote to cut off debate and bring a bill to a vote. The free trade press made much of the tariff as a provocation to both the Southern states and Britain, but sorting out truth from opinion, predictions and partisan analyses from realities, is a difficult business.
McPherson finds slavery the primary difference between Northern and Southern civilization. But much of what was valuable about North and South had little to do with slavery. To the degree that North and South participated in American or Western culture, there will be much of value in each region that can't be related to slavery or free labor.
McPherson's "slavery defined the South" does look quite reductive. It's not the language that other historians would use. But if you disagree with his view, what does account for the differences between the two regions? There is a little to be said for Puritan/Cavalier analyses, but if you think of two twin Huguenots or Ulstermen, one heading for New York or Pennsylvania and the other heading for South Carolina or Georgia, you'll find them and their descendants growing quite different, without any of them encountering Cavaliers or Puritans. Anglicans in Virginia and New York, Congregationalists in Connecticut and Georgia came to diverge radically in their ways of life. Climate may also help explain things but it's not enough either. McPherson may be unfair to the upper South and the border states, but when you consider societies like South Carolina or Mississippi where over half the population was enslaved, and half the white families owned slaves, the difference to other social orders is so striking that it's not easy to reject his argument.
There's nothing more that I can do about your quarrel with McPherson. I recommend you right him nicely and politely with some of your criticisms of his article. If he responds you could have an interesting discussion on your hands. Or if you know any professional historians or graduate students you could take it up with them. I do not recommend calling McPherson a communist or a Marxist or a "rabidly pro-North historian" though.
And so it may have been, but by the time the Morrill bill was turned into law, it was one of the largest tariffs in decades. It had moved well beyond a simple revenue tariff to a protection tariff - an economic distinction that was certainly known to them in the mid 19th century.
Had Southern leaders kept their heads about them, there was no reason to expect massive tariff increases.
There was the Morrill bill. It was well on the way to passage before any southern state seceded, and Lincoln gave every indication he would forward its passage as a protectionist measure well beyond revenue collection.
Indeed, according to one source, there was no effort to get Buchanan to commit himself to vetoing the tariff
The tariff passed the Senate on March 2, 1861. Secession was already a done deal in the majority of the souther states by that time. They saw their affiliation with the US as having been ended and had no reason to continue to lobby its president.
and Robert Toombs voted for the tariff, either because it wasn't regarded as harmful, or because it could be used as a pretext for secession and a provocation to Britain to condemn the unionists.
Toombs' left the Senate sometime in January. The vote on the tariff was on March 2nd.
Courtesy would dictate the use of a more polite phrasing toward him, but in this discussion and for accuracy's sake, my earlier descriptions are perfectly reasonable and factual.