Joan Walsh is Salon's editor at large.

On the 150th anniversary of the start of the Civil War, Americans are engaged in new debates over what it was about. Southern revisionists have long tried to claim it wasn't about slavery, but rather "Northern aggression" – which is a tough sell since they seceded from the Union despite Lincoln's attempts at compromise on slavery, and then attacked the federal Fort Sumter in South Carolina. That would be Southern aggression, by any standard.

But there's still room for smart revisionism. Instead of the traditional view that finds the Civil War a great moral and political triumph, David Goldfield calls it "America's greatest failure" in his fascinating new book, "America Aflame: How the Civil War Created a Nation." It killed a half-million Americans and devastated the South for generations, maybe through today. And while many Northern Republicans came to embrace abolishing slavery as one of the war's goals, Goldfield shows that Southerners are partly right when they say the war's main thrust was to establish Northern domination, in business and in culture. Most controversially, Goldfield argues passionately -- with strong data and argument, but not entirely convincingly -- that the Civil War was a mistake. Instead of liberating African Americans, he says, it left them subject to poverty, sharecropping and Jim Crow violence and probably retarded their progress to become free citizens.

Whether or not you accept that premise – more on that later – Goldfield shows definitively that Northern evangelical Protestants were the moral force behind the war, and once they turned it into a religious question, a matter of good v. evil, political compromise was impossible. The Second Great Awakening set its sights on purging the country of the sins of slavery, drunkenness, impiety -- as well as Catholics, particularly Irish Catholic immigrants. Better than any history I've seen, Goldfield tracks the disturbing links between abolitionism and nativism. In fact, he starts his book with the torching of the Ursuline Convent in Charlestown, Mass. in 1834, a violent attack on Catholics which Goldfield shows was "incited" by Lyman Beecher, the father of the Beecher clan, most of whom turned out to be as anti-Irish Catholic as they were anti-slavery. To evangelical Protestant nativists, Catholicism was incompatible with democracy, because its adherents allegedly gave their loyalty to the Pope, not the president, and the religion's emphasis on obeying a hierarchy made them unfit for self-government. Also, rebellious Irish Catholics didn't show the proper discipline or deference to conform to emerging industrial America. The needs of Northern business were never far from some (though not all) abolitionists' minds.

Still, though nativism was widespread in the North, and within the Republican Party (which  absorbed some old Know-Nothing and nativist Whig party remnants), abolitionism remained at the party's fringe. Most Republicans were seeking compromise, not the abolition of slavery, in the years before the war, including Abraham Lincoln. Our first Republican president didn't like slavery, and he fiercely opposed its extension to the Territories, but he also expressed doubts about African-Americans' capacity for democracy, and he opposed black suffrage. Lincoln supported the Fugitive Slave Act, which let slave-owners call on law enforcement even in free states to capture their runaway "property." (As a lawyer, he'd represented a slave owner trying to recapture a fugitive slave.)

And as a strict constitutionalist, Lincoln resisted abolitionism, because like it or not, the Constitution made room for slavery. The president disliked slavery, but his priority was the union. He famously told abolitionist Republican Horace Greeley (who later turned against Reconstruction and ran for president as a Democrat, abandoning African Americans as did too many other abolitionists): "If I could save the Union without freeing any slave I would do it, and if I could save it by freeing all the slaves I would do it; and if I could save it by freeing some and leaving others alone I would also do that."

In fact, during Lincoln's 1860 presidential campaign, Republicans went so far as to argue that they were the real White Man's Party, because their commitment to keeping the Territories slave-free wasn't about the evils of slavery; it was about keeping the West white, so white families alone could enjoy the bounty of the frontier without competition (except from Indians, who would be eradicated.) Democrats insisted they were the White Man's Party, because slavery liberated white men to be the property owners and entrepreneurs God intended them to be, while an inferior race did their manual labor, for free. Most Republicans and Democrats agreed on white supremacy; they differed on the right way to maintain it.

Yet as the war went on, Lincoln came to see slavery as a moral cause, and he wouldn't entertain compromise armistice proposals that let the South keep black people in bondage. In a book with few heroes, Lincoln emerges as one over time, virtually alone as an American politician in blending compassion for slaves with compassion for white Southerners. It's popular to suggest that had Lincoln lived, Reconstruction would have been more successful. But Lincoln's pattern of compromise throughout his political career makes speculating on what he'd have done very difficult. Goldfield makes clear, though, that Lincoln wanted reconciliation with the South, not Southern humiliation. In his subdued Second Inaugural Address, he refused to blame the war on the Confederacy, or trumpet the righteousness of the Northern cause. Because the Founders legalized slavery, he believed the country, North and South, shared responsibility for it....