I don't recall Buchanan being a major factor. Lincoln was elected on November 6, 1860. South Carolina seceded the next month on December 24.
It seems the secessionists believed Lincoln had no respect for the Constitution or state's rights; and the secessionists were absolutely correct in those beliefs. Lincoln was a self-declared Clayite (a Hamiltonite) who desired the all-powerful, cronyistic, central-planning type of government.
Historian Charles Adams gave this interpretation of the causes of the secession:
"My view that taxes, not slavery, started the American Civil War was vindicated by American Heritage in June of 1996, which said: "The tariff, then nearly synonymous with federal taxes, was a prime cause of the Civil War." I have added and corrected some of the material in that chapter, which the reader should find of interest….
"One of the most popular myths in American history is that the Civil War was started over slavery, and that Lincoln, as the Great Emancipator, drove the nation into a bloody war to break the chains of bondage that shackled over three and a half million black Americans. This popular childhood history story is fable.
"At the eleventh hour before the Civil War began, the Southern slave owners had no need to go to war. They had already won all the battles without firing a shot. With the Supreme Court in their back pocket, with Lincoln and the Congress approving a Constitutional amendment protecting slavery forever, they were undoubtedly the victors in their struggle to preserve the slave system of America. There had to be something else that caused them to fire the first shot."
"During his campaign for the presidency in 1860, Lincoln repeated time and again that he would not interfere with slavery in the South. His first inaugural address said it all. He emphasized the anti-abolitionist policy of his administration, which can be found "in nearly all the published speeches of him who now addresses you. I do but quote from one of those speeches when I declare that 'I have no purpose, directly or indirectly, to interfere with the institution of slavery in the states where it exists. I believe I have no lawful right to do so, and I have no inclination to do so.' "
"Lincoln continued in his inaugural address to assure Southern slave owners that fugitive slaves would be returned. To provide even further assurance, the Congress, with Lincoln's approval, proposed and passed a new Constitutional amendment which declared that the federal government could never interfere with slavery in any state. Even the Supreme Court gave its blessing to slavery in the famous Dred Scott case (1857). All three branches of the federal government had bent over backwards to appease the South over slavery. They could hardly have done much more."
"When the Civil War started, the moral cause of the South was strong – they wanted self-government; there was nothing wrong with that. Why should half the states in the Union be denied the right of self-determination? Is not that a fundamental human and social right?"
"The Civil War was two years old when Lincoln issued the Emancipation Proclamation, and then only after repeated military defeats, and as a last resort to rally the North behind a worthwhile cause. Here are Lincoin's words on the subject:"
"Things had gone from bad to worse, until I felt we had reached the end of our rope on the plan we were pursuing; that we had about played our last card, and must change our tactics or lose the game. I now determined upon the adoption of the emancipation policy."
[Charles W. Adams, "For Good and Evil: The Impact of Taxes on the Course of Civilization." Madison Books, 2nd Ed, 2001, pp.xviii, 329-330]
The New England abolitionist, Lysander Spooner, claimed the government simply replaced one form of slavery, that of the black man, with another form of slavery, that of both white and black men:
"The pretence that the "abolition of slavery" was either a motive or justification for the war, is a fraud of the same character with that of "maintaining the national honor." Who, but such usurpers, robbers, and murderers as they, ever established slavery? Or what government, except one resting upon the sword, like the one we now have, was ever capable of maintaining slavery? And why did these men abolish slavery?Not from any love of liberty in general – not as an act of justice to the black man himself, but only "as a war measure," and because they wanted his assistance, and that of his friends, in carrying on the war they had undertaken for maintaining and intensifying that political, commercial, and industrial slavery, to which they have subjected the great body of the people, both white and black. And yet these impostors now cry out that they have abolished the chattel slavery of the black man – although that was not the motive of the war – as if they thought they could thereby conceal, atone for, or justify that other slavery which they were fighting to perpetuate, and to render more rigorous and inexorable than it ever was before. There was no difference of principle – but only of degree – between the slavery they boast they have abolished, and the slavery they were fighting to preserve; for all restraints upon men's natural liberty, not necessary for the simple maintenance of justice, are of the nature of slavery, and differ from each other only in degree." [Lysander Spooner, "No Treason: The Constitution of No Authority." By the Author, 1867, pp.56-57]
Mr. Kalamata
So the bottom line is Southern Secession was driven by the feeling that Lincoln and the Republican controlled legislature would take action against the slave institution in the South.