Some commenters on my posts on secession (here and here) doubt my claim that the southern states seceded in 1861 for the purpose of preserving slavery. After all, they point out, Abraham Lincoln and the Republicans had promised not to abolish slavery in the states where it existed. This is a common point advanced by those want to claim that slavery was not the main cause of the Civil War. Indeed, it was first advanced by apologists for the Confederate cause in the immediate aftermath of the War in order to paint the Confederacy in a more positive light by demonstrating that it was fighting for "states' rights" rather than slavery. But the claim doesn't withstand scrutiny.

Confederate leaders repeatedly stated in 1861 that the threat Lincoln's election posed to slavery was the main reason for secession. In January 1861, soon-to-be Confederate President Jefferson Davis said that his state had seceded because "She has heard proclaimed the theory that all men are created free and equal, and this made the basis of an attack upon her social institutions; and the sacred Declaration of Independence has been invoked to maintain the position of the equality of the races." Davis was referring to well-known speeches by Lincoln and other Republicans citing the Declaration in criticism of slavery. Confederate Vice President Alexander Stephens similarly said that "slavery . . . was the immediate cause of the late rupture and present revolution" and that protecting it was the "cornerstone" of the new Confederate government. Many other Confederate leaders made similar statements.

Why did Lincoln's election cause them to fear for the future of slavery? It is true that the Republicans did not plan to abolish slavery in the near future. But white southerners still saw Lincoln's election on an antislavery platform as a serious threat to the "peculiar institution." Whatever their position on slavery where it already existed, the Republicans were firm in their commitment to preventing its spread to the vast new territories acquired by the US in the Mexican War. That, in fact, was the main point of the Republican platform. Slaveowners believed that an end to the expansion of slavery threatened their economic interests. In addition, the creation of numerous new free states without the admission of any new countervailing slave states would erode slaveowners' influence in congressional and presidential elections and potentially pave the way for abolition in the future.

Perhaps even more important, most white southerners didn't trust Lincoln's assurances that he wouldn't move against slavery in the South. After all, this was the same man who had famously said that "this government cannot endure permanently half slave and half free," and that "the opponents of slavery" should "arrest the further spread of it, and place it where the public mind shall rest in the belief that it is in the course of ultimate extinction." He meant that blocking the expansion of slavery would eventually put pressure on southern states to abolish it "voluntarily." But slaveowners suspected that he and other Republicans would attack the Peculiar Institution directly if they got the chance. Within the Republican Party, Lincoln was a relative moderate. More radical Republicans wanted stronger, more immediate action against slavery. And their influence within the party might grow over time.

Finally, slaveowners feared that Lincoln's election would undermine slavery in border states such as Maryland, Missouri, Kentucky, Tennessee and even Virginia, which already had many fewer slaves than the Deep South. By using patronage to promote the growth of Republican parties in these states and relaxing enforcement of the Fugitive Slave Act, a Republican-controlled federal government could eventually force these states to abolish slavery. Without strong federal enforcement of the Fugitive Slave Act, slaves from border states adjacent to slave states could more easily escape to the North and border state slaveowners would have incentives to sell their slaves to the deep south, where slaves couldn't run away as easily; this, of course, would undermine the institution of slavery in the border states. If the Republicans could turn the border states into free states and do the same with all the new states to be established in the West, they could create a large enough majority of free states to enact a constitutional amendment banning slavery throughout the country.

It was to head off these various threats to slavery that the southern states chose to secede in 1861. For documentation of all these points, including quotes from Confederate leaders, see historian William Freehling's excellent book, The South vs. the South.

Ultimately, slavery would probably have lasted longer if the South hadn't seceded in 1861. The Confederates clearly underestimated the North's will to fight (just as northerners underestimated that of the Confederates). Nonetheless, they did have reason to see Lincoln's election as a serious longterm threat to slavery. And that fear underlay the decision to secede.