The War of South Carolina Aggression
The miliarism behind what James McPherson has called The War of Southern Aggression -- or, even more specifically, The War of South Carolina Aggression -- has roots much older and deeper than that War or even the slave system.
I always start with Albion's Seed and the British roots of American culture.
In England, the military is a traditional career for the *second* son -- because in the central & southern counties of the English "heartland", inheritance is by primogeniture and the first son gets the lot. The original English settlers in Virginia and points South were from this part of England, and though they themselves were mostly younger sons they reproduced the inheritance structures they were familiar with. So in addition to being a culture that tolerated a lot of individual violence, they also tended to have a lot of men interested in joining the military for lack of other inheritance.
In contrast, the Puritan settlers of New England came from East Anglia, where inheritance was traditionally partible. Every son got *something* and was expected to make that into more (by trade, etc.), so there was no automatic pipeline into military careers. East Anglian culture also stressed restraint of individual violence, turning people away from the idea that fighting was the way to solve problems.
The later groups of settlers -- Quakers from the North Midlands who settled in the Delaware Valley and were even more anti-military than New Englanders, immigrants from the English-Scottish Border who moved to the American backcountry and were even more violence-tolerant than the Virginian Cavaliers -- only emphasized the original division between the more military South and less military North.