I'm a Northerner, from Michigan. Of course it was about states' rights. It took living in Virginia for a few years for me to come to that understanding.
If you actually want to know what the was was about, read from an expert. Alexander H. Stephens Cornerstone Address, March 21, 1861:
"But not to be tedious in enumerating the numerous changes for the better, allow me to allude to one other-though last, not least: the new Constitution has put at rest forever all the agitating questions relating to our peculiar institutions-African slavery as it exists among us-the proper status of the negro in our form of civilization. This was the immediate cause of the late rupture and present revolution. Jefferson, in his forecast, had anticipated this, as the "rock upon which the old Union would split." He was right. What was conjecture with him, is now a realized fact. But whether he fully comprehended the great truth upon which that rock stood and stands, may be doubted. The prevailing ideas entertained by him and most of the leading statesmen at the time of the formation of the old Constitution were, that the enslavement of the African was in violation of the laws of nature; that it was wrong in principle, socially, morally and politically. It was an evil they knew not well how to deal with; but the general opinion of the men of that day was, that, somehow or other, in the order of Providence, the institution would be evanescent and pass away. This idea, though not incorporated in the Constitution, was the prevailing idea at the time. The Constitution, it is true, secured every essential guarantee to the institution while it should last, and hence no argument can be justly used against the constitutional guarantees thus secured, because of the common sentiment of the day. Those ideas, however, were fundamentally wrong. They rested upon the assumption of the equality of races. This was an error. It was a sandy foundation, and the idea of a Government built upon it-when the "storm came and the wind blew, it fell."
Our new Government is founded upon exactly the opposite ideas; its foundations are laid, its cornerstone rests, upon the great truth that the negro is not equal to the white man; that slavery, subordination to the superior race, is his natural and moral condition. [Applause.] This, our new Government, is the first, in the history of the world, based upon this great physical, philosophical, and moral truth. This truth has been slow in the process of its development, like all other truths in the various departments of science. It is so even amongst us. Many who hear me, perhaps, can recollect well that this truth was not generally admitted, even within their day. The errors of the past generation still clung to many as late as twenty years ago. Those at the North who still cling to these errors with a zeal above knowledge, we justly denominate fanatics. All fanaticism springs from an aberration of the mind; from a defect in reasoning. It is a species of insanity. One of the most striking characteristics of insanity, in many instances, is, forming correct conclusions from fancied or erroneous premises; so with the anti-slavery fanatics: their conclusions are right if their premises are. They assume that the negro is equal, and hence conclude that he is entitled to equal privileges and rights, with the white man.... I recollect once of having heard a gentleman from one of the Northern States, of great power and ability, announce in the House of Representatives, with imposing effect, that we of the South would be compelled, ultimately, to yield upon this subject of slavery; that it was as impossible to war successfully against a principle in politics, as it was in physics or mechanics. That the principle would ultimately prevail. That we, in maintaining slavery as it exists with us, were warring against a principle-a principle founded in nature, the principle of the equality of man. The reply I made to him was, that upon his own grounds we should succeed, and that he and his associates in their crusade against our institutions would ultimately fail. The truth announced, that it was as impossible to war successfully against a principle in politics as well as in physics and mechanics, I admitted, but told him it was he and those acting with him who were warring against a principle. They were attempting to make things equal which the Creator had made unequal."
free dixie,sw