Though Southern apologists have repeatedly said that slavery was not the cause of the Civil War, they are I believe mistaken. And that is the kindliest interpretation I can make of the facts. The reasons given at the time for secession are far more openly "pro-slavery". Now there were economic factors involved (certainly, if the slaves had all been freed and no compensation offered to the slave holders, it would have cost them a great deal of money). But at the core, the Southern politicians of the time seem to have recognized that it was slavery (or rather, the rise of an anti-slavery movement outside their own slave holding states) that was the reason they had to secede.
What follows are extracts from the articles of secession for Texas, Georgia, Mississippi and South Carolina. The full texts for these articles can be found at http://sunsite.utk.edu/civil-war/reasons.html
From the Texan articles of secession:
By the disloyalty of the Northern States and their citizens and the imbecility of the Federal Government, infamous combinations of incendiaries and outlaws have been permitted in those States and the common territory of Kansas to trample upon the federal laws, to war upon the lives and property of Southern citizens in that territory, and finally, by violence and mob law, to usurp the possession of the same as exclusively the property of the Northern States.
From the Georgian articles of secession:
Such are the opinions and such are the practices of the Republican party, who have been called by their own votes to administer the Federal Government under the Constitution of the United States. We know their treachery; we know the shallow pretenses under which they daily disregard its plainest obligations. If we submit to them it will be our fault and not theirs. The people of Georgia have ever been willing to stand by this bargain, this contract; they have never sought to evade any of its obligations; they have never hitherto sought to establish any new government; they have struggled to maintain the ancient right of themselves and the human race through and by that Constitution. But they know the value of parchment rights in treacherous hands, and therefore they refuse to commit their own to the rulers whom the North offers us. Why? Because by their declared principles and policy they have outlawed $3,000,000,000 of our property in the common territories of the Union; put it under the ban of the Republic in the States where it exists and out of the protection of Federal law everywhere; because they give sanctuary to thieves and incendiaries who assail it to the whole extent of their power, in spite of their most solemn obligations and covenants; because their avowed purpose is to subvert our society and subject us not only to the loss of our property but the destruction of ourselves, our wives, and our children, and the desolation of our homes, our altars, and our firesides. To avoid these evils we resume the powers which our fathers delegated to the Government of the United States, and henceforth will seek new safeguards for our liberty, equality, security, and tranquillity.
From the Mississippi articles of secession:
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.
From the South Caroline articles of secession:
The General Government, as the common agent, passed laws to carry into effect these stipulations of the States. For many years these laws were executed. But an increasing hostility on the part of the non-slaveholding States to the institution of slavery, has led to a disregard of their obligations, and the laws of the General Government have ceased to effect the objects of the Constitution. The States of Maine, New Hampshire, Vermont, Massachusetts, Connecticut, Rhode Island, New York, Pennsylvania, Illinois, Indiana, Michigan, Wisconsin and Iowa, have enacted laws which either nullify the Acts of Congress or render useless any attempt to execute them. In many of these States the fugitive is discharged from service or labor claimed, and in none of them has the State Government complied with the stipulation made in the Constitution. The State of New Jersey, at an early day, passed a law in conformity with her constitutional obligation; but the current of anti-slavery feeling has led her more recently to enact laws which render inoperative the remedies provided by her own law and by the laws of Congress. In the State of New York even the right of transit for a slave has been denied by her tribunals; and the States of Ohio and Iowa have refused to surrender to justice fugitives charged with murder, and with inciting servile insurrection in the State of Virginia. Thus the constituted compact has been deliberately broken and disregarded by the non-slaveholding States, and the consequence follows that South Carolina is released from her obligation
Observing the *forms* [emphasis in the original] 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.
The kindliest interpretation that I can make of the Southern Civil War apologists is that they are sadly misinformed. The harshest interpretation is that they are attempting to spread a Big Lie: that the Civil War was the fault of the North, and that the racism and pro-slavery stances of the Southern states had nothing to do with the treason that was committed.