The subtitle of Harry Stout’s new history of the Civil War hints at large, possibly unrealizable ambitions. If any war in American history insists on moral analysis and judgment, it is surely the Civil War. For a decade before the first shots were fired at Fort Sumter, North and South had been engaged in a fierce, partisan, but fundamentally moral debate about the nature of America. Was the United States a true democracy, whose civic promises could be claimed by all citizens regardless of race? Or was it an aristocratic republic, in which a privileged caste enjoyed its rights through slave labor.

Slavery was the engine that drove the country to war, even though politicians in the 1850s often tried to conceal that fact under the legalistic jargon of states’ rights and popular sovereignty. Even when the war began in 1861, virtually no one in the North or South openly called it a war over slavery; Union and Secession, not abolition, were the slogans of the day. Still, as the war grew more and more deadly,and especially after Lincoln issued the Emancipation Proclamation in late 1862, only the moral urgency of abolition seemed to justify its immense cost. As Lincoln aptly put it in his second inaugural address: “All knew that this interest [slavery] was somehow the cause of the war.”

Given that profoundly moral “cause,” then, one might expect “Upon the Altar of the Nation” (Viking, 552 pages, $29.95) to be mostly concerned with the war’s relationship to slavery. But Mr. Stout – a historian of American religion at Yale and the editor of “The Works of Jonathan Edwards” – approaches the subject from a valuably different perspective. He is primarily interested in both sides’ conduct of hostilities, as judged by traditional notions of just war, and in the failure of the country’s moral authorities – the clergy and the press – to concern themselves with that conduct.The Civil War was fought in a just cause, Mr. Stout argues, but it is by no means clear that it was a just war. “It is possible, and, I believe, reasonable,” he writes, “to conclude that the right side won in spite of itself.”

In making this argument, Mr. Stout draws on concepts of just war that date back to Thomas Aquinas. Traditional just-war theory discriminates between two kinds of right: jus ad bellum, the right to make war, and jus in bello, the right conduct of war. In the case of the Civil War, the former is much more straightforward than the latter. The preservation of the Union and the abolition of slavery were very compelling reasons for the North to make war on the South. But the very importance of the cause, Mr. Stout shows, meant that virtually no responsible parties, on either side, concerned themselves with how the war was being fought.

Instead, Mr. Stout shows, through detailed examination of contemporary newspapers and sermons, the responsibility of criticism gave way to the most blatant cheerleading. He writes:

Moral ‘reflection’ abounded, to be sure, but only in ways that reinforced the ‘right’ side. Despite unprecedented losses, hard questions of cause and conduct were seldom raised. Moral arbiters on both sides fell back on stock rhetorical affirmations coming dangerously close to cliches.

As a result, there was no moral friction to slow the war’s momentum toward slaughter and savagery.

The Civil War was, after all, not just the bloodiest war in American history but in many ways the first modern war. Both sides employed new firearms and artillery that made traditional frontal assaults hopeless. But as usually happens, the generals – inexperienced West Point graduates at best, patronage appointees at worst – kept fighting like it was the last war, the Mexican War, in which daring attacks were the key to victory.The result was the unprecedented, and still unfathomable, slaughter of battles like Antietam and Gettysburg.

The key insight of Mr. Stout’s innovative study is that the very cost of such battles, far from provoking civilian scrutiny of military strategy, only increased both sides’ reliance on thoughtless religious and patriotic rhetoric. As befits a religious historian, Mr. Stout is especially interested, and especially disappointed, in the way the clergy fell into lockstep with the government and the military. Abolitionists and white supremacists were equally ferocious in their certainty that God smiled on their cause. For Southern ministers, this was a war to preserve a nascent Christian Republic, as the Presbyterian pastor Robert Dabney claimed:

If any modern nation can possibly be placed in the situation of Judea when oppressed by Antiochus, when the Maccabees, although priests, judged it their religious duty to take up the sword, our people are now in a case equally urgent.

At the same time, the Northern Unitarian chaplain William Scandlin declared: “Enshrined within the civil and religious liberties of this nation, are the highest and brightest hopes of the world. Hence our duty is to preserve this Christian legacy in a Christian spirit.”

This kind of passivity, Stout shows, did not just stop the clergy from criticizing the conduct of the war; it positively encouraged both sides to become more absolute in their claims, more unconstrained in their tactics. If the Civil War was dictated by providence, after all, then no method of winning it could be considered unholy. And while the South committed its share of atrocities – the burning of Chambersburg, the concentration-camp-like prison at Andersonville – it is the North that bears the brunt of Mr.Stout’s criticism. Exactly because he knows the North’s cause was just, he is pained by its cruel tactics, which fell far outside the boundaries of jus in bello.

After the North’s battlefield debacles in the first two years, Lincoln, Grant, and Sherman were determined to make war on the South’s whole economy and population,using every means short of outright massacre to bring the Confederacy to its knees. Mr. Stout usefully reminds us that it was their very indifference to suffering that enabled Grant to win his bloody battles, and Sherman to conduct his March to the Sea. At every point, the North’s leaders decided that the end – the preservation of the Union and the abolition of slavery – justified the means. “If the people raise a howl against my barbarity and cruelty,” Sherman wrote coldly, “I will answer that war is war, and not popularity-seeking.”

The Civil War is one of the most romanticized chapters in our history, and Mr. Stout does a great service in reminding us of its actual barbarity. (It would be hard to imagine anyone reading this book and then rushing off to a fun weekend of re-enacting Chancellorsville.) But it is doubtful whether the terms of Mr. Stout’s moral critique finally allow him to plumb the depths of the war’s tragedy. In holding the war up to a textbook standard of justice, Mr. Stout naturally finds it wanting. But has any war, before or after, ever met those ideal criteria? Has any belligerent ever stopped short of using all the means in its power for victory? And in this particular case, would it have been more just for the North to refrain from “hard war” tactics, thus risking a prolonged war, a Copperhead victory in 1864, and the possible permanence of slavery? Finally, Mr. Stout’s procedural righteousness comes to seem inadequate to the moral complexity of the Civil War. If the clergy and press of 1861 had been filled with men like him, their record might have been more honorable, but it’s unlikely that history would have been any different.

akirsch@nysun.com