On May 30, 1878, the Abraham Lincoln Post No. 13 of the veterans of the Grand Army of the Republic invited Frederick Douglass to speak at its annual Memorial Day celebration in New York. Douglass took the occasion to reflect on the previous decade’s civil war, particularly in light of the recent attempts by leading secessionists to whitewash the cause for which they’d fought by erasing slavery from their memoirs and history books. Southern writers were already asserting that they had fought nobly and heroically, if in vain, for the “lost cause” of states’ rights and limited government. But Douglass was having none of it. The bloody struggle between the North and the South, he insisted, was “a war between the old and new, slavery and freedom, barbarism and civilization.” The sentimental urge to honor the courage of the men who fought on both sides was all well and good, he said, but remember:

There was a right side and a wrong side in the late war, which no sentiment ought cause us to forget, and while today we should have malice toward none and charity for all, it is no part of our duty to confound right with wrong, or loyalty with treason.

Elizabeth R. Varon quotes Douglass’s speech in the introduction to her 2008 book Disunion! The Coming of the American Civil War, and she quotes it again in the conclusion to her latest one, Armies of Deliverance: A New History of the Civil War. By bookending her two-volume history of the war with the same quotation, Varon makes her point effectively but without fanfare: This was a momentous struggle over slavery, and in that struggle the South was on the wrong side. But what about the right side, presumably the North? If the wrong side stood for the preservation of slavery, what did the right side stand for?

Varon goes about answering this question in a distinctive way. Taking her cue from the British intellectual historian Raymond Williams, she chooses a pair of keywords to tell the two halves of her story. For the origins of the war, the word is “disunion,” the multiple meanings of which she traces over time until, by the 1850s, it had come to mean “secession.” For the war itself, the word is “deliverance,” and she tracks how different Americans used the word in their distinct ways to explain the conflict. For Confederates, it meant deliverance from the Yankee invaders; for antislavery Northerners, it meant deliverance from the “Slave Power”; and for slaves, it meant deliverance from 250 years of bondage.

Varon does not want to confuse rhetoric with reality. Again, she quotes Douglass: “Union and Disunion are but words—the thing is slavery.” But she is vague about precisely how slavery proved so divisive that Americans ended up going to war with one another. Above all, she cannot explain why hundreds of thousands of enslaved blacks, nonslaveholding Southerners, Northern Democrats, and antislavery Republicans came together to defeat the slaveholders’ rebellion. This coalition made the Civil War, in large measure, a conflict between slaveholders and nonslaveholders.

Armies of Deliverance is a compelling rendition of a familiar tale. Chapter by chapter, Varon takes us through the most important events of the war, from the First Battle of Bull Run in the summer of 1861 to the assassination of Abraham Lincoln and the beginnings of Reconstruction almost four years later. Her accounts of the major battles are admirably crisp and efficient. Without getting bogged down in arcane scholarly debates, she succinctly informs readers of the controversies that divide military historians before offering her own invariably sensible judgments. Her former colleague the late Russell Weigley once noted the “chronic indecisiveness” of a war’s battles, and following his lead, Varon is not inclined to overstate the military significance of any single engagement; she even doubts whether Gettysburg was the turning point that other historians make it out to be. What mattered, she insists, was the cumulative effect of four years of fighting that steadily wore down the Confederate Army until, in the end, Robert E. Lee had no choice but to surrender to his Union counterpart, Ulysses S. Grant, at Appomattox.

The battle scenes are skillfully interspersed between accounts of the political events and social history of the war. The Union defeat at the First Battle of Bull Run, for example, leads into a discussion of the earliest stirrings of federal emancipation policy. George B. McClellan’s failure during the Peninsula Campaign prompts Union leaders to shift to a policy of hard war, which includes a more aggressive attack on slavery. The battle at Antietam spurs Lincoln to announce the Emancipation Proclamation. The Union victories at Gettysburg and Vicksburg in the summer of 1863 happen as the first regiments of the United States Colored Troops are taking the field. News of the impressive performance of black troops at Port Hudson and Milliken’s Bend discredits the simultaneous outburst of anti-war violence that culminates in New York City’s horrific draft riots. The Overland Campaign—the long and brutal slugfest between Grant and Lee in the spring of 1864—generates a wave of war weariness that threatens Lincoln’s chances for reelection.

Varon does a fine job of showing how deeply the fortunes of war influenced the fortunes of politics. By August 1864, it looked as though the Democrats might succeed in replacing the Republican Lincoln with George McClellan, an anti-emancipation general running on an anti-war platform. Yet by September, news came that Sherman had taken Atlanta, Farragut had captured Mobile Bay, and Sheridan had routed the Confederates in the Shenandoah Valley. Lincoln and the Republicans were reelected, and within months they succeeded in getting the 13th Amendment through Congress. By the time Lee surrendered and Lincoln was assassinated, the abolition of slavery was all but certain.

In the hands of a less skillful writer, these numerous shifts from the battlefront to emancipation policy to politics could easily seem bumpy and disjointed, but Varon’s transitions are always smooth and effective. What makes her account even more impressive is the way she uses major battles to introduce important aspects of the war’s social history. Her account of the Battle of Shiloh, for example, opens out into the history of Civil War hospitals, the work of the Sanitary Commission, and the role of women, especially nurses.

Varon is determined to tell as much of the story as possible through the voices of the men and women who experienced it. No other general history of the war so lavishly quotes from the letters of soldiers, the diaries of women, the self-serving excuses of incompetent generals, the editorials of partisans, the denunciations of critics, and the speeches of politicians. The highest ideals held by the combatants come through as clearly as the most repellent outbursts of racist demagoguery. Through these voices, readers can get a feeling for the ground-level, tactile experience of the war as well as the dramatic debates in the halls of Congress. The myriad horrors of battle are vividly rendered, and so is the 1864 presidential election.

Indeed, sometimes there is too much of a good thing. Varon quotes a dozen soldiers when two or three will do. There is also a bit too much reaction-shot history: An event is described, often briefly, and then is followed by page after page of responses to it, often culled from old newspapers that are now readily available in digitized form. For example, her characteristically lucid account of Lincoln’s Proclamation of Amnesty and Reconstruction—in which he spelled out his generous plan for reincorporating the seceded states into the Union—is followed by a long series of entirely predictable reactions. The Republicans said this, the Democrats said that, and the radicals and the conservatives said other things.

That Varon’s new book includes so many voices matters, in part, because of the choices she had to make about what not to include in her 400-page history. Military historians will wonder why there’s so little discussion of strategy and tactics. Logistics are reduced to a brief (if fascinating) account of how City Point, Virginia, became the base for supplying Grant’s army during the siege of Petersburg. There’s not much diplomatic or legal history, either, and important developments in economic policy get short shrift. The creation of a federal monetary union through the Legal Tender Act is relegated to a footnote. There’s virtually no account of how the North and the South financed their wars. And there’s no political economy at all. Varon does not explain the extraordinary capacity of the North’s free-labor economy to flourish even as it paid the staggering price of fighting a war, nor does she contrast that with the collapse of the South’s economy and the startling inability of an agricultural society to feed itself.

Given the Confederacy’s obvious significance to any history of the Civil War, it is surprising how little space Varon devotes to it. This may be because her organizing device, the keyword “deliverance,” works better for the North than the South. Confederate generals who embarked on invasions of the Union sometimes made blustery announcements that they had come to Kentucky or Maryland to deliver the oppressed citizenry from the scourge of Yankee tyrants, but for the most part, the rhetoric of deliverance was used by the North.

The Republicans did believe they were going to help deliver the mass of Southerners from the clutches of an overbearing Slave Power, but Varon repeatedly describes the Slave Power as a “conspiracy theory.” It was no such thing. The Slave Power was the name antislavery Northerners gave to something most historians recognize as very real—the disproportionate power exercised by the slaveholders over every branch of the federal government. From 1790 to 1860, nearly every president was either a slaveholder or a proslavery Northerner. The Supreme Court was dominated by proslavery justices. The House of Representatives and the Electoral College were skewed by the Constitution’s three-fifths clause, which enhanced Southern political influence over Congress and the presidency. The foreign- policy apparatus was dominated by imperial-minded slaveholders and their allies. This was the Slave Power, and its opponents had clear and convincing explanations for the source of its strength and compelling reasons for wanting to destroy it.

Similarly, Varon claims the Northern war effort was driven by the misapprehension that the Southern masses were “deluded” into supporting the Confederacy. There are two problems with what she calls the Republicans’ “deluded masses theory.” First, although some Northerners spoke of white Southerners that way, especially during the second year of the war, they were far more likely to describe Southern whites as oppressed. These are two very different things. Varon even acknowledges the brutal lengths Confederate authorities went to in their determined effort to silence Southern Unionists, who were prosecuted, harassed, threatened, driven from their homes, beaten into submission, or murdered.

This suggests the second problem with the “deluded masses theory.” Varon claims that Southern whites, far from being deluded, were genuinely united in support of the Confederacy, whereas her own evidence shows they were seriously divided. During the secession crisis, for example, nonslaveholders were considerably more hostile to disunion than were slaveholders, and in three of the states where they held considerable power—Kentucky, Maryland, and Missouri—they prevented their states from seceding. In the largest slave state, Virginia, nonslaveholders in the west seceded from the slaveholder-dominated counties to the east and created the state of West Virginia. After secession, too, there remained considerable Unionist enclaves in eastern Tennessee and western North Carolina, which the Confederacy went to great lengths to suppress. In the end, some 300,000 Southern whites fought for the Union. These were staggering losses for the Confederacy, and they suggest why Northerners had good reason to believe that white Southerners were not unified in support of the slaveholders’ rebellion.

“Deliverance” offers some insights into how many in the North viewed the Union’s efforts, but as an organizing theme, its usefulness is limited. The “deluded masses theory” is even less useful; at best it explains the thinking of some Northerners about some Southerners. Certainly by 1862 no one in the North could seriously entertain the proposition that 4 million black slaves had somehow been “deluded” into supporting the Confederacy. The slaves made their Unionist sympathies clear from the start, and Republicans were counting on that sympathy all along.

If we demote the significance of the deliverance theme, there is another way to organize the impressive evidence that Varon has accumulated. The Civil War was an explosive example of the one thing that American mythology says this country never has: class conflict—or, at least, class politics—in this case pitting slaveholders against nonslaveholders. Start with Varon’s observation that most of the Unionist sentiment in the South was antislaveholder rather than antislavery. She makes a similar point about the War Democrats in the North, who had no interest in emancipating the enslaved but had been infuriated by the treason of the Southern slaveholders. If antislaveholder and antislavery sentiment could be united in defense of the Union, the Slave Power could be defeated.

Lincoln and the Republicans understood this. To be sure, they never separated their determination to suppress the Slave Power from their hatred of slavery itself. They went to war to uphold what they believed was an antislavery Constitution and to restore the antislavery union that the founders intended to create. They made it clear that they would put down the slaveholders’ rebellion at all costs, and they could do so because in 1861 they had taken control of the presidency and (thanks to the secession of 11 slave states) both houses of Congress.

But to win the war, they needed more than congressional majorities; they needed allies, and their natural allies in the struggle against the Slave Power were the nonslaveholders in the South as well as the North. “A privileged class has existed in this country from an early period of its settlement,” New York Senator William Seward declared in 1855. “The slaveholders constitute that class.” The irrepressible conflict over slavery was best understood as a “conflict between the privileged and the unprivileged classes of this republic.”

The rallying cry for the coalition of the unprivileged classes was “Union.” Lincoln went to great lengths to hold the Northern War Democrats in the coalition, even as they recoiled from the Emancipation Proclamation, by appealing to their Unionism. In the summer of 1863, in the aftermath of the Draft Riots, Lincoln made it clear that opponents of emancipation still had good reason to support the war. “You say you will not fight to free negroes,” he wrote in an open letter to War Democrats. “Some of them seem willing to fight for you; but, no matter. Fight you, then, exclusively to save the Union.” By the end of the war, hundreds of thousands of War Democrats, unwilling to “fight to free negroes,” nevertheless fought and died to suppress the slaveholders’ rebellion.

The same can be said of those Southern whites who remained loyal to the Union. The pages of antebellum Southern history are crammed with conflicts between the Black Belt slaveholders and the up-country yeomen. Those nonslaveholders brought decades of political hostility toward the planters with them into the Civil War, and hundreds of thousands joined the Union Army. When they went into battle, their bullets were as important in undoing slavery as those of the most ardent antislavery soldiers in their ranks.

Then, of course, there were the millions of enslaved people who constituted the Confederacy’s greatest internal enemy. As soon as the war began, slaves ran to the Union lines first by the hundreds, then by the thousands, then by the tens of thousands. (Half a million were inside Union lines by the time the war ended.) Slaves fed the Union Army critical intelligence on the whereabouts of Confederate troops and supplies. At home, they disrupted the routine on plantations whenever the masters and their sons went to war.

By late 1861, Republicans commonly referred to these enslaved people as the most reliably loyal Unionists in the South. Over 100,000 of those who reached Union lines donned Yankee uniforms, marched into battle, and aimed their rifles at the Confederates who were fighting to keep their parents, siblings, wives, and children in slavery. It was the greatest social revolution in American history.

No single element of this coalition—the antislavery Republicans, the War Democrats, the Southern Unionists, the self-emancipated slaves—could have succeeded by itself in destroying the largest, wealthiest slave society on earth, and yet each was indispensable to the success of the broader coalition. By naming a common enemy—the privileged class of slaveholders—the Republican Party was able to build and then steer a coalition of whites and blacks, racists and anti-racists, toward the systematic destruction of slavery. When the nonslaveholders of western Virginia petitioned for admission to the Union as a separate state, the Republicans in Congress required them to formally abolish slavery first. The hundreds of thousands of Southern whites and Northern Democrats who fought only to restore the Union were directed by their superiors to emancipate slaves as they marched through the South, whether they supported the idea or not. When slaves ran to the Union lines, the soldiers they encountered were under orders to admit them.

As with any such coalition, there were internal tensions. Some soldiers—mostly War Democrats—turned escaping slaves away, especially in the early months of the war. But in 1862, the Republican-controlled Congress made it a crime for soldiers to do so. Union soldiers from slave states openly resisted the policy of emancipation until the very end, yet pressure from slaves below and policy-makers above ultimately overwhelmed their opposition. Lincoln and the Republicans had organized an army of 2 million nonslaveholders who would eventually wipe out the South’s privileged class and liberate 4 million slaves.

The history of the Civil War is, in large measure, the history of this coalition as it evolved over four years of fighting. Although the Union Army was at first composed almost exclusively of Yankees, there was tension between those (mostly Democrats) motivated solely by the desire to save the Union and others (mostly Republicans) who believed that to save the Union it was necessary to undermine slavery. The policy of military emancipation adopted by the Republicans in the first months of the war was designed to weaken but not destroy slavery. Then with the Emancipation Proclamation of January 1, 1863, the war became a revolution, even as the scope of the coalition widened. It was no longer enough to undermine slavery; from that point on, Lincoln and the Republicans determined that the restoration of the Union required slavery’s complete destruction. As more and more black and white Southerners filled the ranks of the Union Army, the internal conflict between antislavery and antislaveholder troops intensified. In Kentucky, white Southern-born troops sometimes fell into open fighting with Northern-born soldiers over the treatment of black enlistees and their families. But Union authorities doubled down, silencing, jailing, court-martialing, and dishonorably discharging soldiers who openly opposed emancipation. Despite internal divisions, the Union and the coalition that emerged to protect it survived.

The same could not be said for the South. The Confederate Army that surrendered at Appomattox had been depleted by the mass desertion of nonslaveholders from its ranks. The Union Army, by contrast, had been replenished by nearly 180,000 African-American soldiers, allied with tens of thousands of Southern whites, War Democrats, and resolutely antislavery Republicans. In the presidential election of 1864, 80 percent of soldiers cast their ballots, matching the highest turnouts in American history, and as many as 75 percent of their votes went to Lincoln. In the end, destroying slavery and suppressing the Slave Power amounted to the same thing.

You can’t see this if you start from the assumption that the Slave Power was simply a conspiracy theory. In Varon’s account, the Republicans went to war driven by the assumption that the Southern masses were deluded. Her secessionists, on the other hand, went to war driven by the delusion that the Republicans hated slavery and were determined to do what Lincoln said they would do: put slavery “on a course of ultimate extinction.” This puts Varon perilously close to the long-discredited revisionist historians who attributed the Civil War to a blundering generation of politicians who, addled by their own propaganda, hurled the country into a needless conflict. Varon doesn’t believe that, but her own reasoning implies it, and it detracts from what is otherwise an outstanding book—one of the best accounts of the Civil War we have. She is at her best when she reminds us, as Frederick Douglass did long ago, that there was a right side and a wrong side in that war.