I assume that "we" is the Royal "We."
The guy is a Professor of History at the University of Virginia, Mr. Jefferson's University. So he brings those credentials to the table. I provided a link to an Amazon page where his most recent book is reviewed and argued about. (Did you bother to look? Let me guess: it was too much trouble.) That book is a 1200+ page tome about pre-"Civil War" politics, and you want me to present his argument here in a response to you? My one sentance attempt would be: The "Civil War" was caused by the breakdown of the two party system. Does that really help you?
My point was not whether Holt is correct, or those who suggest slavery, or economics are correct. My point was that there are very highly educated people in the field who do not think slavery was the primary cause, and it is foolish to dismiss them out of hand.
ML/NJ