Reading the posts on here, you get an idea of why the history of the civil war is muddled. Saying slavery was a side issue is quite frankly whitewashing the reality, that slavery was a major issue of the civil war. The idea that slavery was dying is problematic (two economists won the nobel prize in that field not long ago, for showing it wasn’t dying). It is true that in the ‘old south’ , they made a lot more money selling slaves than in growing crops (In a biography of Washington, they quote him back in the late 18th century, that having slaves was costing him money, that the cost of maintaining slaves wasn’t worth it). The money was made, though, selling slaves into new markets, which was the big, contentious battle of the 19th century, the expansion of slavery. Even with the missouri compromise, those making money in the slave trade were not happy, they wanted slavery expanded to all new territories, which anyone with half a brain can figure out why, because it was very, very lucrative to sell slaves into new markets. Slavery was dying in the old south in terms of agriculture, but the fact is that outside the 'old south, it was thriving.
States rights were invoked because the south saw slaves as property, and felt that the states had the right to determine where property should be sold, and some used the full faith and credit clause to argue that states banning slaveholding were denying that .
Yes, the South was angry about the Tariffs, the north to feed their mills and such wanted southern raw goods (cotton, lumber, sugar, other things), the South wanted to sell the goods on the open market, to England, at better prices than they could get up north, and there was a legitimate grievance there. However, the south never even gave negotiations a chance, Lincoln took office in March, 1861 and it wasn’t long after that the states seceded…and the debate over secession started before Lincoln was elected, but took fire afterwords, because despite the fact that Lincoln made clear abolitionism wasn’t something he was looking to promote, the southern states assumed he was going to try and abolish slavery, so that tells me that slavery was a major issue. Later on in the war, Lincoln made only two demands of the south, in terms of ending the conflict, and that was allegiance to the union and the end of slavery, and the confederacy refused those terms.
It also is unknown whether the Corwin amendment would have passed or not, the fact that there were more non slave states wouldn’t necessarily mean it would go to defeat. The reality is that most states, even those where abolitionist sentiment were strong, would not want to sacrifice the union for slavery, and it is possible that the Corwin amendment would have passed. simply to try and preserve the union. Common history has made this gigantic pitch about the abolitionist north and the evil slave holding south, which is as wrong as the common position from folks down south that it was all ‘states rights’, if to make a choice between slavery being legal and the dissolution of the union, the legislatures in those states, and the people in congress, might likely have voted for it.
Some of the issues of the civil war were also cultural. Whether or not a third of the families down south owned slaves (which means 2/3rd’s did not, a large majority), the reality of the south is that the power was based in the well off planter class, who saw themselves as aristocracy, blue bloods,it was a de facto aristocracy where the well off landowners controlled most of the power (and voting was based on property ownership, and I seem to recall that you needed to have property above a certain level, and it was not a small amount). To them (Bruce Catton wrote about this, as did James McPherson) the northerners were crude industrialists, the population a combination of recent immigrants and crude common farmers, and part of the civil war wasn’t just slavery, but also, at least in the opinion of some historians, maintaining the privilege and power of a de facto landed aristocracy, they feared what they saw in the north (in some cases , with some real world cases, the political boss system like Tammany Hall and such), with ‘mob rule’ and so forth.
Saying it was all about slavery, with the heroic north wanting to abolish it and the south wanting to keep it is factually not correct, but saying slavery was not a major issue if not the primary issue is also just as equally wrong. Slavery was a major issue, if not the main issue, and it manifested itself in several ways, if it didn’t play out to the traditional narrative.
As far as why the soldiers fought, especially those who had no slaves and were very much hurt by slavery economically, Shelby Foote I think did the best job documenting it, most of them felt like they had to fight for their country, for their place, I don’t know how much slavery itself influenced them as much as feeling like it was a duty.The planter class also did a major PR effort, they told the non slaveholders/less well off folk “you are one of us, you are a proud son of the south, descendents of the aristocracy” and it was pretty effective in getting them to fight for something that in a sense, hurt them (ie slavery, assuming it was a major factor).
There is a lot of revisionism, there have been politicians and school boards that have promoted the idea that slavery wasn’t so bad, that “x thousands of slaves fought for the confederacy”, so it couldn’t have been that bad (leaving out that happened in the latter part of the war, when some southern states offered slaves who fought their freedom if they fought for the south), or that 180,000 black soldiers fought for the union, many of them escaped slaves…in many ways, it is kind of a retelling of the “song of the South’s” version of slavery, happy slaves singing in the cotton fields.
As far as racism goes, neither north nor south had a monopoly on that. Many in the north who fought to end the civil war were fearful of black slaves being freed (part of the cause of the draft riots were that Irish immigrants, besides having to fight while the rich paid someone to take their place, was the fear of black ex slaves bringing down wages; it is telling that during the draft riots targets of the mobs rage were things like orphanages for black kids, black run businesses, black houses and so forth). The difference between the south and north has been that in the south, it was a lot more overt; the south had jim crow, legalizing segregation or more importantly, mandating it, while in the north, it was simply part of the landscape. In the cities, blacks tended to live in certain areas, were often not allowed to rent or own in areas other than ‘black districts’, that is the reality. While lynching was not common in the north (other than if you classify, for example, Indiana as being in ‘the north’, where lynchings were common) the fact is that the north had no stomach to try and pass anti lynching laws, and didn’t actively go after it until the civil rights era.