Paul Krugman succinctly puts to bed any obfuscation of Southern aggression:
But it may be worth delving a bit deeper into the background here. Why did slavery exist in the first place? Why was it confined to only part of the United States? And why were slaveholders willing to start a war to defend the institution, even though abolitionism was still a fairly small movement and they faced no imminent risk of losing their chattels?
Let me start with an assertion that may be controversial: The American system of chattel slavery wasn’t motivated primarily by racism, but by greed. Slaveholders were racists, and they used racism both to justify their behavior and to make the enslavement of millions more sustainable, but it was the money and the inhumane greed that drove the racist system.
Labor was scarce in pre-Civil War America, so free workers earned high wages by European standards.
Landowners, of course, didn’t want to pay high wages. In the early days of colonial settlement, many Europeans came as indentured servants — in effect, temporary serfs. But landowners quickly turned to African slaves, who offered two advantages to their exploiters: Because they looked different from white settlers, they found it hard to escape, and they received less sympathy from poor whites who might otherwise have realized that they had many interests in common. Of course, white southerners also saw slaves as property, not people, and so the value of slaves factored into the balance sheet of this greed-driven system.
Anyone who believes or pretends to believe that the Civil War was about states’ rights should read Ulysses S. Grant’s memoirs, which point out that the truth was almost the opposite. In his conclusion, Grant noted that maintaining slavery was difficult when much of the nation consisted of free states, so the slave states in effect demanded control over free-state policies. “Northern marshals became slave-catchers, and Northern courts had to contribute to the support and protection of the institution,” he wrote.
And the war happened because the increasingly empowered people of the North, as Grant wrote, “were not willing to play the role of police for the South” in protecting slavery.
So yes, the Civil War was about slavery — an institution that existed solely to enrich some men by depriving others of their freedom. And there’s no excuse for anyone who pretends that there was anything noble or even defensible about the South’s cause: The Civil War was fought to defend an utterly vile institution.
Historians have known this for 160 years, but the Southern landowning class has successfully confused the issue for generations, as far as most people understand it. It's always money. Just like the Republican Party's craziness today.