The American Civil War was not a war over slavery. Slavery was actually a side issue. The war was actually a fight over taxes.
That's exactly what the Michigan middle school history taught us in the late 1960's. The Emancipation Proclamation (similar to an executive order) wasn't signed until a few years after the war had started.
Then why do so many of the articles of secession explicitly mention slavery rather than taxation? Those were their chance, like in the Declaration of Independence, to express their highest ideals. Some, like Florida and Louisiana, essentially said the union with the United States was dissolved without giving reasons. On the other hand Mississippi said "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."
The taxation reason appears to be mainly post war revisionism. Preservation of slavery was the reason why the southern states left in 1861.
Western states, the old Northwest, had much in common with the Southern states when it came to taxes and tariffs. Ohio farmers were as hurt by East Coast manufacturer's tariffs as the Southern planter. They had much in common—but one thing stood out:
Slavery.
It was the constant defense of that Peculiar Institution that drove the Deep South states to abandon the rest. My Alabama seceded on January 11, 1861, and Lincoln wasn't even inaugurated yet. The RICH planters who ran the state met in Montgomery and drafted up a document explaining their decision—it was about slavery as THE issue.
The original document:
Whereas, the election of Abraham Lincoln and Hannibal Hamlin to the offices of president and vice-president of the United States of America, by a sectional party, avowedly hostile to the domestic institutions* and to the peace and security of the people of the State of Alabama, preceded by many and dangerous infractions of the constitution of the United States by many of the States and people of the Northern section, is a political wrong of so insulting and manacing a character as to justify the people of the State of Alabama in the adoption of prompt and decided measures for their future peace and security, therefore:Be it declared and ordained by the people of the State of Alabama, in Convention assembled, That the State of Alabama now withdraws, and is hereby withdrawn from the Union known as "the United States of America," and henceforth ceases to be one of said United States, and is, and of right ought to be a Sovereign and Independent State.
Sec 2. Be it further declared and ordained by the people of the State of Alabama in Convention assembled, That all powers over the Territory of said State, and over the people thereof, heretofore delegated to the Government of the United States of America, be and they are hereby withdrawn from said Government, and are hereby resumed and vested in the people of the State of Alabama.
And as it is the desire and purpose of the people of Alabama to meet the slaveholding States of the South, who may approve such purpose, in order to frame a provisional as well as permanent Government upon the principles of the Constitution of the United States.Remember that Virginia, Tennessee, North Carolina and Arkansas—Confederate states with the least amount of slaves—that joined the original Confederacy after Lincoln called for an army of 75,000 volunteers to conquer the Deeper South.
*Negro Slavery