Plantation agriculture rapidly exhausted the soil. The sectional balance of Congress aside, planters needed new land to grow the cotton that secured their influence on the national (and international) stage. As Karp explains, “Slaveholders in the 1850s seldom passed up an opportunity to sketch the inexorable syllogism of King Cotton: The American South produced nearly all the world’s usable raw cotton; this cotton fueled the industrial development of the North Atlantic; therefore, the advanced economies of France, the northern United States and Great Britain were ruled, in effect, by Southern planters.” The backlash to slavery — the effort to restrain its growth and contain its spread — was an existential threat to the Southern elite.
It was the realization of that threat with the election of Abraham Lincoln — whose Republican Party was founded to stop the spread of slavery and who inherited a federal state with the power to do so — that pushed Southern elites to gamble their future on secession. They would leave the union and attempt to forge a slave empire on their own.
The point of this compact history, with regard to the present, is that it is irresponsible to talk about civil war as a function of polarization or division or rival ideologies. If those things matter, and they do, it is in how they both reflect and shape the objective interests of the people and factions in dispute.
Which is to say that if you’re worried about a second Civil War, the question to ask isn’t whether people hate each other — they always have, and we tend to grossly exaggerate the extent of this country’s political and cultural unity over time — but whether that hate results from the irreconcilable social and economic interests of opposing groups within the society. If it must be one way or the other, then you might have a conflict on your hands.
That’s where America was with slavery. That’s why our actual Civil War has been called the impending crisis. I’m not sure there’s anything in American society right now that plays the same role that the conflict over slavery did. Whatever our current challenges, whatever our current divisions, I do not think the United States is where it was in 1860. We have enough problems ahead of us already without having to worry about war breaking out here.