Peter Turchin, writing for Bloomberg:
Slavery had been a divisive force since the inception of the Republic. For 70 years, the elites always managed to find a compromise. During the 1850s, however, intra-elite cooperation unraveled. On several occasions Congress was on the brink of a general shootout. (As one senator noted about his “armed and dangerous” colleagues, “The only persons who do not have a revolver and a knife are those who have two revolvers.”) Although slavery was the overriding issue dividing the elites, they also differed over tariffs and cultural attitudes toward immigration. In the decade before the Civil War these centrifugal forces tore apart the two-party system. The Democratic Party split into its Northern and Southern factions, while the Whigs simply disintegrated.
A very thought-provoking piece.