Mencius Moldbug explains how the War of Secession came about:
At the time of American independence, there was little or no proslavery ideology. American slavery was an accident, an outlier. It was an African institution which had spread to the English colonies via Portugal and Spain. It survived because English property and contract law of the time was so strong that it frowned not at all on contractual servitude. This was easily extended to Negro slaves purchased from the existing Spanish asiento trade, though they had signed no contract of indenture. Slavery existed at first because no one had the power to ban it or to confiscate slaves. Before the American Rebellion it was gradually regularized — in all states, not just the South — by legal recognition of actual fact. It was, in short, an unprincipled exception to the democratic enthusiasms of the 18th century.
So, for example, a Virginian slaveholder like Jefferson could write a prohibition of slavery into the law that established the Northwest Territory, because the issue at the time was not a bone of contention. Statesmen of the early Republic, North and South, generally saw slavery as an artifact of history which was undesirable and fated, somehow, to disappear.
All this changed in the ’20s, and still more in the ’30s, with the rise of abolitionism. Imported from England and associated, as we would expect, with Quakers, Unitarians, Methodists, etc, etc, abolitionism was the first great cause of the democratic era. Its original exponents, as we would expect, were highly moral and principled intellectuals, such as John Quincy Adams.
There were two basic problems with abolitionism.
One: it could not be seen as anything but an attack on the South, the weaker party, by the North, the stronger party. Once the lines of sectional politics were clear, as Jefferson saw clearly in 1820, the question of whether a new state would allow slavery was the question of which bloc would get its two new Senators.
Two: the North had no legal basis whatsoever for this attack. The idea that the Federal government had the power to end slavery and free the slaves was roughly as foreign to antebellum constitutional law as the proposition that Barack Obama could order Rush Limbaugh hanged at dawn, “just because he’s an asshole,” is to ours.
Southern politicians, writers and ministers found the moral defense of slavery in the context of democracy and Christianity a difficult problem, but not at all impossible for the sinuous. But they found the legal defense of slavery no problem at all, because the law was on their side from day one.
Northern politicians, writers and ministers had exactly the opposite problem. While the American mores of 1850 were not quite the same as ours, moral condemnation of slavery came almost as naturally then as it does now. However, said moral condemnation created the urge to actually do something about the problem. For which the North had no legal standing at all.
During the 1840s and 1850s, the antislavery movement spread far beyond the handful of Massachusetts intellectuals who were the original abolitionists. And its features became extremely unattractive. Because it had no legal means to proceed, it resorted to illegal ones. Because the truth was that the North was attacking the South and trying to abolish slavery, its politicians had to assert that the South was attacking the North and trying to propagate slavery. Conspiracy theories abounded — such as Lincoln’s completely false charge that the Dred Scott decision was a conspiracy between Douglas, Buchanan, Taney and Pierce to bring about national slavery, as wild a lie as anything in American political history.
As the ideology of antislavery spread West, it passed from those who hated slavery because they loved Negroes as fellow men, to those who hated slavery because they didn’t want Negroes around. (Lincoln, with typical dexterity, managed to convince his audiences that he was in both categories.) Thus the free-state Kansas constitution prohibited Negroes free or slave, as did that of Oregon. By 1860, little that is human or humane can be found in the antislavery movement. Its engine runs on pure chimp rage. As Pierce’s speech shows, it took no hindsight to detect the growing smell of blood.
Responsible Northern statesmen, typically Democrats or “old line” Whigs, saw where things were going, and with their old Southern Unionist friends did their best to shut the antislavery agitation off. This was generally taken by antislavery men, and by your less scrupulous historians, as complicity with the infamous Slave Power.
So, for example, the authors of the Dred Scott decision had no thought of instituting slavery in Vermont. Their goal was to drive a legal nail into the coffin of the antislavery movement, allowing a country in which the map of slavery had been finally and completely outlined (after Kansas, there were no remaining territorial quarrels) to return to politics as usual. But every attempt of this type was no more than political fuel to the antislavery machine.
Southerners developed the increasingly beleaguered sense of nationalism that terminated in secession. They had two choices, neither good. If they compromised and accepted Northern demands, despite the essential asymmetry of the situation, they gave in to force and fed a crocodile. The next round of agitation would demand more. If Southerners resisted, being the hot-blooded people they were, or even raised the ante, they were conjuring the specter of the Slave Power and contributing to Northern paranoia.
Moldbug heartily recommends George Lunt’s Origin of the Late War:
I cannot even fathom the quantity of testicular fortitude required to publish this sort of material in Boston in 1865. Origin of the Late War is simply a wonderful book; it has both judgment and immediacy, detail and passion. I recommend it highly. If you only read one primary source on the War of Secession, this should probably be the one.