Note: This subject is fully and ably covered by Ta-Nehisi Coates at The Atlantic;
click here for his article, "What This Cruel War Was Over."
Over the years, various revisionists have argued that slavery was not the sole or even a major reason for the secession of the South -- economics, unfair restriction of trade, states' rights, and unfair taxation are reasons given. Those may indeed have been factors, but South Carolina, where the first shots of the war were fired at Fort Sumter, leaves no room for doubt in its "Declaration of the Immediate Causes Which Induce and Justify the Secession of South Carolina from the Federal Union," published on December 24, 1860.
Click here to read that document. (The word "slavery" -- or "slave" or "slaves" or "slaveholding" -- occurs 16 times.)
Here's part of the declaration:
The ends for which the Constitution was framed are declared by itself to be "to form a more perfect union, establish justice, insure domestic tranquility, provide for the common defence, promote the general welfare, and secure the blessings of liberty to ourselves and our posterity."
These ends it endeavored to accomplish by a Federal Government, in which each State was recognized as an equal, and had separate control over its own institutions. The right of property in slaves was recognized by giving to free persons distinct political rights, by giving them the right to represent, and burthening them with direct taxes for three-fifths of their slaves; by authorizing the importation of slaves for twenty years; and by stipulating for the rendition of fugitives from labor.
We affirm that these ends for which this Government was instituted have been defeated, and the Government itself has been made destructive of them by the action of the non-slaveholding States. Those States have assume the right of deciding upon the propriety of our domestic institutions; and have denied the rights of property established in fifteen of the States and recognized by the Constitution; they have denounced as sinful the institution of slavery; they have permitted open establishment among them of societies, whose avowed object is to disturb the peace and to eloign the property of the citizens of other States. They have encouraged and assisted thousands of our slaves to leave their homes; and those who remain, have been incited by emissaries, books and pictures to servile insurrection.
For twenty-five years this agitation has been steadily increasing, until it has now secured to its aid the power of the common Government. Observing the forms of the Constitution, a sectional party has found within that Article establishing the Executive Department, the means of subverting the Constitution itself. A geographical line has been drawn across the Union, and all the States north of that line have united in the election of a man to the high office of President of the United States, whose opinions and purposes are hostile to slavery. He is to be entrusted with the administration of the common Government, because he has declared that that "Government cannot endure permanently half slave, half free," and that the public mind must rest in the belief that slavery is in the course of ultimate extinction.
This sectional combination for the submersion of the Constitution, has been aided in some of the States by elevating to citizenship, persons who, by the supreme law of the land, are incapable of becoming citizens; and their votes have been used to inaugurate a new policy, hostile to the South, and destructive of its beliefs and safety.
On the 4th day of March next, this party will take possession of the Government. It has announced that the South shall be excluded from the common territory, that the judicial tribunals shall be made sectional, and that a war must be waged against slavery until it shall cease throughout the United States.
The guaranties of the Constitution will then no longer exist; the equal rights of the States will be lost. The slaveholding States will no longer have the power of self-government, or self-protection, and the Federal Government will have become their enemy.
Sectional interest and animosity will deepen the irritation, and all hope of remedy is rendered vain, by the fact that public opinion at the North has invested a great political error with the sanction of more erroneous religious belief.
UPDATE: Here's an excerpt from a companion piece, "A Declaration of the Immediate Causes which Induce and Justify the Secession of the State of Mississippi from the Federal Union":
Our position is thoroughly identified with the institution of slavery—the greatest material interest of the world. Its labor supplies the product which constitutes by far the largest and most important portions of commerce of the earth. These products are peculiar to the climate verging on the tropical regions, and by an imperious law of nature, none but the black race can bear exposure to the tropical sun. These products have become necessities of the world, and a blow at slavery is a blow at commerce and civilization. That blow has been long aimed at the institution, and was at the point of reaching its consummation. There was no choice left us but submission to the mandates of abolition, or a dissolution of the Union, whose principles had been subverted to work out our ruin…
Click here for a link to a document consisting of the declarations of Georgia, Mississippi, South Carolina, Texas, and Virginia.
UPDATE: Here's another piece, from Louisiana's declaration:
As a separate republic, Louisiana remembers too well the whisperings of European diplomacy for the abolition of slavery in the times of annexation not to be apprehensive of bolder demonstrations from the same quarter and the North in this country. The people of the slave holding States are bound together by the same necessity and determination to preserve African slavery.
And another, from Alabama:
Upon the principles then announced by Mr. Lincoln and his leading friends, we are bound to expect his administration to be conducted. Hence it is, that in high places, among the Republican party, the election of Mr. Lincoln is hailed, not simply as it change of Administration, but as the inauguration of new principles, and a new theory of Government, and even as the downfall of slavery. Therefore it is that the election of Mr. Lincoln cannot be regarded otherwise than a solemn declaration, on the part of a great majority of the Northern people, of hostility to the South, her property and her institutions—nothing less than an open declaration of war—for the triumph of this new theory of Government destroys the property of the South, lays waste her fields, and inaugurates all the horrors of a San Domingo servile insurrection, consigning her citizens to assassinations, and. her wives and daughters to pollution and violation, to gratify the lust of half-civilized Africans.
And here's Texas:
...in this free government all white men are and of right ought to be entitled to equal civil and political rights; that the servitude of the African race, as existing in these States, is mutually beneficial to both bond and free, and is abundantly authorized and justified by the experience of mankind, and the revealed will of the Almighty Creator, as recognized by all Christian nations; while the destruction of the existing relations between the two races, as advocated by our sectional enemies, would bring inevitable calamities upon both and desolation upon the fifteen slave-holding states....
UPDATE, AUGUST 15, 2015: Colonel Ty Seidule, professor and Head of the Department of History at the United States Military Academy at West Point:
Was the American Civil War fought because of slavery? More than 150 years later this remains a controversial question.
Why? Because many people don't want to believe that the citizens of the southern states were willing to fight and die to preserve a morally repugnant institution. There has to be another reason, we are told. Well, there isn't.
The evidence is clear and overwhelming. Slavery was, by a wide margin, the single most important cause of the Civil War -- for both sides. Before the presidential election of 1860, a South Carolina newspaper warned that the issue before the country was, "the extinction of slavery," and called on all who were not prepared to, "surrender the institution," to act. Shortly after Abraham Lincoln's victory, they did.
Click here for the video.
