During the American Civil War, did those in the South believe that they were fighting to remain true to the beliefs of the Founding Fathers or were they intentionally breaking away from that ideology and attempting to form their own nation/ideology entirely?

Part 1 of 4: The Trouble with Original Intent

It's complicated. I don't normally like to lead with theory stuff, but this is one of those cases where it makes more sense to start abstract and then drill down.

Diving the original intent, vision, or ideology of the founders involves a tremendous amount of interpretation that is often left unstated but has significant fall out for all that follows. There's no singular vision of the founders to refer to, except maybe that independence from the British Empire was a good idea, circa summer of 1776. Disputes over what independence means, the best way to form a government, the most legitimate basis for authority, and a tremendous tangle of issues were only held at bay temporarily by the Revolutionary War. It's true that the founders, whoever and by whatever metric we decide membership in that group, agree on some things some of the time and don't have perfectly unique, sui generis, conceptions of the nation, but there's enough disagreement to make appeal to a founding tradition, ideals, etc. deeply problematic.

Those disagreements happen in public as well as behind closed doors. Arguments over, say, the meaning of the Constitution date to before ratification. Some of the men at Philadelphia abandoned the effort early and others refused to sign the final product. They continue during ratification, though this is often obscured beneath the standard version that The Federalist is the most authoritative take and carried the day. In Massachusetts, anti-federalists oppose ratification in part because they understand the Constitution as a proslavery document, as in this open letter from Consider Arms (who did more than consider them in Shay's Rebellion), Malachi Maynard (ditto), and Samuel Field. Their beefs:

In the first place-as direct taxes are to be apportioned according to the numbers in each state, and as Massachusetts has none in it but what are declared freemen, so the whole, blacks as well as whites, must be numbered; this must therefore operate against us, as two fifths of the slaves in the southern states are to be left out of the numeration; consequently, three Massachusetts infants will increase the tax equal to five sturdy, full grown negroes of theirs, upon who work every day in the week for their masters

In other words, the 3/5 clause for apportioning direct taxes (the feds just send the states a bill) subsidizes slavery at the expense of the free people of Massachusetts. So the Constitution is underwriting slavery with built-in tax breaks.

It gets worse. Looking at the unamendable prohibition on ending slave imports before 1808, the writers declare:

It was not controverted in the Convention, but owned that this provision was made purely that the southern states might not be deprived of their profits arising from that most nefarious trade of enslaving Africans. The hon. Mr. King himself, who was an assistant in forming this constitution, in discoursing upon this epithet, nefarious, which carries with it the idea of something peculiarly wicked and abominable: and indeed we think it deserving of this and every odious epithet which our language affords, descriptive of the iniquity of it, a constitution, which gives license to a measure of this short-How is it possible we could do it consistent with our ideas of government? consistent with the principles and documents we endeavour to inculcate upon others?

And what if the slaves revolted? What does the vision embodied by the Constitution say happens then?

let us suppose for once, a thing which is by no means impossible, viz. that those Africans should rise superior to all their local and other disadvantages, and attempt to avenge themselves for the wrongs done them? Or suppose some potent nation should interfere in their behalf, as France in the cause of America, must we not rise and resist them? Would not immediately call forth the whole force of the country, if needed, to oppose them, and so attempt more closely to rivet their manacles upon them, and in that way perpetuate the miseries of those unhappy people?

I've picked Massachusetts because it's a fairly big state at the time and has already enacted abolition of slavery through its 1780 constitution, albeit a little unwittingly and not officially until a judge said the new state constitution meant as much in 1783. Similar arguments were made at the state's ratification convention, both by the three authors aforementioned and others. Troubled by them, particularly the words of Quaker James Neal and his apparent success in rallying the Bay State's Quakers to the anti-federalist cause, Jeremy Belknap writes to Benjamin Rush in Pennsylvania to ask how his Quakers parse the slave trade provision. Rush writes back:

I am very happy in being able to inform you that they [the Quakers] are all (with an exception of three or four persons only) highly foederal. -There was a respectable representation of that Society in our Convention, all of whom voted in favor of the New Constitution. They consider very wisely that the Abolition of slavery in our country must be gradual in order to be effectual, and that the section of the Constitution which will put it in the power of Congress twenty years hence to restrain it altogether, was a great point obtained from the Southern States. The appeals therefore that have been made to the human & laudable prejudices of our quakers by our Antifoederal writers, upon the Subject of Negro Slavery, have been treated by that prudent Society with Silence and Contempt.

You might expect proslavery and antislavery groups to read the same constitution and come to opposite conclusions. They do; the slavery issues that make the Constitution a difficult sell in New England are put up as selling points in South Carolina. But between Rush's Pennsylvania Quakers and Belknap's Massachusetts Quakers, we have two antislavery groups with proven records -Pennsylvania enacted a gradual abolition measure in 1780- who read the same text and come to opposite conclusions. In both cases, the parties are aware of and participant in debate among the Constitution's actual authors. They can't agree if it's proslavery or antislavery.

We can say that these are not important people. The anti-federalists may not genuinely be founders the same way the federalists are and the federalists, by definition, support the Constitution. But the federalist movement breaks up in the Washington years over just what the Constitution does and doesn't mean. The principle case of this is establishing a national bank which Alexander Hamilton favors because he deems it within the ambit of the necessary & proper and general welfare clauses of the constitution, while Jefferson and Madison did not but rather viewed it as a kind of perversion. Both men took different positions once they were president.

So to divine a founding ideology, we would have to ask at minimum: Which founders? When? About what? And why? The answers to these questions, in practical terms and conventionally, come down to The ones who agree with me, on the occasions that they agree with me, and about whatever I'm talking about right now. Antislavery Americans keep invoking the founders to support them for the entire span of slavery being an active subject of controversy in the United States. Proslavery Americans do the same. Neither is entirely wrong, but both are actively constructing politically useful pasts and ignoring contradictions or problematic positions both between founders and in the interface between their positions and the founders stated policies, actions, and inaction.

It's customary in for Americans of all political stripes to revere "the founders" in a civic religion kind of way as the national forefathers, just as much in 1860 as in 1997. One may have gripes against a particular founder -until recently, Alexander Hamilton was the most popular one to just outright dislike, but the Ten Dollar Founding Father Without a Father has had a bit of a renaissance in the last twenty years- but as a group, they're great and good men who agree with us and we should agree with them. Therefore, the speaker's politics command a patriotic imprimatur denied to those the speaker opposes. To put it in pop culture terms: the speaker's position is the one Captain America endorses and the other side is the one that gets Cap's fist to the face.