Above all, it was a time when Christianity allied itself, in the most unambiguous and unconditional fashion, to the actual waging of a war. In 1775, American soldiers sang Yankee Doodle; in 1861, it was Glory, glory, hallelujah! As Stout argues, the Civil War “would require not only a war of troops and armaments … it would have to be augmented by moral and spiritual arguments that could steel millions of men to the bloody business of killing one another...” Stout concentrates on describing how Northerners, in particular, were bloated with this certainty. By “presenting the Union in absolutist moral terms,” Northerners gave themselves permission to wage a war of holy devastation. “Southerners must be made to feel that this was a real war,” explained Colonel James Montgomery, a one-time ally of John Brown, “and that they were to be swept away by the hand of God, like the Jews of old.” Or at least offered no alternative but unconditional surrender. “The Southern States,” declared Henry Ward Beecher shortly after Abraham Lincoln’s election to the presidency, “have organized society around a rotten core,—slavery,” while the “north has organized society about a vital heart, —liberty.” Across that divide, “God is calling to the nations.” And he is telling the American nation in particular that, “compromise is a most pernicious sham.”
But Southern preachers and theologians chimed in with fully as much fervor, in claiming that God was on their side. A writer for the Southern quarterly, DeBow’s Review, insisted that since “the institution of slavery accords with the injunctions and morality of the Bible,” the Confederate nation could therefore expect a divine blessing “in this great struggle.” The aged Episcopal bishop of Virginia, Richard Meade, gave Robert E. Lee his dying blessing: “You are engaged in a holy cause.”
When, by 1864, defeat was looking the Confederacy in the eyes, the arms of the pious dropped nervelessly to their sides, and they concluded that God was deserting them, if not over slavery, then for Southern unbelief. “Can we believe in the justice of Providence,” lamented Josiah Gorgas, the Confederacy’s chief of ordnance, “or must we conclude we are after all wrong?” Or even worse, wailed one despairing Louisianan, “I fear the subjugation of the South will make an infidel of me. I cannot see how a just God can allow people who have battled so heroically for their rights to be overthrown.”
Total war, as Yale law professor James Whitman has recently written, was the result of politics, and particularly by the movement of governments in the 19th century away from monarchy and toward popular democracy. So long as government had been the private preserve of kings, then wars had been the sport of monarchs, and were fought as though they were princely trials by combat or a species of civil litigation. The only class of people likely to suffer severely by them was the nobility. The scope of war was limited simply because war was understood to be the prerogative of kings. [emphasis added]
But once democratic governments began to shoulder the monarchs aside—once governments became “of the people, by the people, for the people” and involved the entire people of a nation and not just a handful of aristocrats—war became the instrument of entire populations. No solitary monarch could now call them off; no gentlemen’s agreement could limit their scope. Wars became wars of nations against nations, waged for principles abstract enough to command everyone’s assent, and therefore all the more impossible to win short of the annihilation—not just the defeat—of an enemy. Not religion, but democracy made it necessary to invoke “millennial nationalism,” in order to recruit sufficient mass resources for new mass wars. Theories about justice in war or debates about the proportionality with which war could be waged would only serve as obstacles in the path to unconditional victory.
Appeals to divine authority at the beginning of the Civil War fragmented in deadlock and contradiction, and ever since then, it has been difficult for deeply rooted religious conviction to assert a genuinely shaping influence over American public life.
In exposing the shortcomings of religious absolutism, the Civil War made it impossible for religious absolutism to address problems in American life—especially economic and racial ones—where religious absolutism would in fact have done a very large measure of good. Some leaders, Martin Luther King prominent among them, have since invoked Biblical sanction for a political movement, but that has mostly been tolerated by the larger, sympathetic environment of secular liberalism as a harmless eccentricity which can go in one ear and out the other.
More and more, it can seem that King's appeal to Christian heritage and theological reasoning has been swept under the rug in popular presentations of who he was.
One of the observations Mark Noll made in The Civil War as a Theological Crisis was that the majority of folks in the United States were evangelical Protestant but the slavery issue didn't get clearly settled because the question about race wasn't settled. Although both sides could insist that they were proving their respective positions from the Bible there was an impasse. Noll noted that although there were theological traditions that had arrived at the conclusion that slavery in general could be permitted but that race-based slavery as it was practiced in the United States was immoral, these views were sidelined. Why? Because Protestants in that time weren't going to take the theological advice of Catholics and Jews. On the other hand, many nominally Protestant groups that had landed at a comparable conclusion were considered outside the pale of traditional Trinitarian orthodoxy.
As Noll noted in his substantially longer book America's God, even though both evangelicals and Catholics viewed republicanism with deep skepticism Americans embraced it and were convinced the flaw of uneducated mob rule was not ultimately going to be a big problem. For European theologians the aim was "just" to avoid the arbitrary dictates of kinds and aristocrats on the one hand, and mob dynamics on the other. So long as you didn't end up in either of those ditches just about anything in the middle was probably okay. Americans found a way ...
then again, reverse-engineering the kind of theology or ideology you want in order to justify what you've already committed to doing is pretty much human nature.