In his second inaugural address, delivered as the Civil War neared its end, Abraham Lincoln turned not to politics but to theology.

“Both read the same Bible and pray to the same God, and each invokes His aid against the other,” he observed, acknowledging the deep religious divide that had fueled the conflict. Rather than celebrating Union victory, Lincoln presented the war as a divine reckoning for the nation’s sin of slavery, declaring that “if God wills that it continue until all the wealth piled by the bondsman’s two hundred and fifty years of unrequited toil shall be sunk, and until every drop of blood drawn with the lash shall be paid by another drawn with the sword,” then so be it. Quoting Psalm 19:9, he reminded his audience that “the judgments of the Lord are true and righteous altogether.”

Yet Lincoln did not arrive at this moment of weighty religious insight in a vacuum. As historian Richard Carwardine demonstrates in Righteous Strife: How Warring Religious Nationalists Forged Lincoln’s Union, the president’s theological framing emerged within a broader religious culture that shaped Americans’ views of the conflict. What they saw was something more than a political crisis or military struggle. It was a profound spiritual reckoning.

Through a sweeping examination of sermons, church schisms, and theological debates, Carwardine reveals how faith shaped both Union and Confederate identities, giving their clash a distinctly religious character. Although Christian nationalism has become a vague and often politicized buzzword in contemporary discourse, Carwardine uses the term with greater precision. He defines it as a “fusion of religious purpose and nationalist vision, where religious and national identities not only coexist but are mutually reinforcing.”

From the nation’s founding to the Civil War, he argues, religion provided a sacred, even transcendent framework for defining America’s identity and charting its course. In shaping both the moral cause of abolition and the Confederate justification for secession, the Civil War was not merely a contest over warring economic systems, cultural identities, or constitutional interpretations. As Righteous Strife masterfully shows, it was also a battle between competing religious nationalisms.

Carwardine expands the conventional narrative of the Civil War’s origins by emphasizing theological divisions over slavery and escalating schisms within Protestant churches. In his telling, the slavery debate did more than fracture political alliances. It also divided religious communities, reshaping denominational landscapes and fueling sectional tensions.

In America’s early years, a broad national consensus tolerated Christian slave owning (whether approvingly, begrudgingly, or indifferently). By the 1830s and 1840s, however, this consensus had collapsed, giving way to irreconcilable divisions that fractured evangelical churches along North-South lines. The rupture was especially pronounced among Methodists, Baptists, and Presbyterians, whose national organizations struggled to maintain unity in the face of deepening theological fault lines.

The Methodists divided in 1844 after their General Conference demanded that a slave-owning bishop, James O. Andrew, resign. Southerners interpreted this decision as proof that abolitionist theology was corrupting their denomination. Similarly, the Baptists split in 1845 due to conflict about missionary organizations appointing slave owners leading to the formation of the Southern Baptist Convention​.

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These theological divisions did not remain within the era’s churches. They also played out within the ranks of the Whig and Democratic parties.

Building on his earlier classic work, Evangelicals and Politics in Antebellum America, Carwardine observes that the Whigs, with their emphasis on moral improvement and societal reform, attracted Congregationalists, reformist Presbyterians, and Unitarians. Members of these groups tended to view state action as a means of fostering virtuous citizenship. By contrast, the Democratic Party appealed to those who viewed government-backed moral reform as a threat to both religious and individual liberty and a distortion of Christian witness. Evangelicals who opposed Sabbatarian laws and temperance measures, along with many Roman Catholics and frontier Methodists, gravitated toward Andrew Jackson’s vision of democracy, which championed laissez-faire governance while still affirming Christianity’s essential role in American life.

As Carwardine illustrates, these competing visions became deeply embedded in party politics and beyond, intensifying sectionalism and setting the stage for an eventual crisis of union. In his analysis, the North’s reformist, postmillennialist outlook, rooted in evangelical Protestantism, envisioned America as a moral agent, divinely tasked with advancing God’s kingdom through progressive social change. By contrast, the South’s religious culture fused an honor-based ethos with a theological defense of slavery as divinely ordained. Southern ministers argued that slavery was sanctioned by Scripture and essential for maintaining Christian civilization, portraying abolitionism as a theological heresy​.

By the 1850s, this proslavery theology had hardened into a near-universal doctrine, with many Southern clergy framing secession as a sacred duty to defend a godly society against Northern radicalism​. As Carwardine observes, “Each side was convinced of the righteousness of its own reforming impulse and the defective morality of the other.” In short, this religious divergence was not merely a symptom of sectional tensions but a central catalyst of America’s bloodiest and most devastating war.

Carwardine is not the first historian to examine the religious dimensions of the Civil War. Mark Noll has explored the theological fractures over slavery. Harry S. Stout has analyzed the war’s moral justifications. James P. Byrd has examined the Bible’s influence on wartime rhetoric. And Drew Gilpin Faust has considered how the conflict reshaped American attitudes toward death and the afterlife.

Carwardine builds on this scholarship by centering the concept of religious nationalism, arguing that faith was not merely a cultural backdrop but a decisive force in shaping political allegiance, national identity, and Lincoln’s evolving leadership. Ultimately, he presents the Civil War as a profoundly religious crisis, not only in its theological debates over slavery but also in its competing visions of America’s divine purpose, particularly as they suggested analogies to Old Testament Israel. As Carwardine notes, such analogies cut both ways: If likening America to Israel implied receiving God’s blessings, it also implied the possibility of provoking his judgment. While the notion of America as a chosen nation dates back to its founding, the Civil War revealed deep fractures over what it truly meant to be chosen. Or, as Lincoln put it, whether the nation was an “almost chosen people.”

Many previous accounts of the Civil War tend to dismiss presidential proclamations made by Lincoln and James Buchanan for a national day of humiliation, fasting, and prayer. In these treatments, they appear as mere footnotes or political maneuvers. Carwardine, however, underscores their deep spiritual significance for ordinary Americans, for whom these proclamations were more than symbolic gestures. They spoke to widespread anxieties that had citizens turning to God, first to avert war and then to ensure the Union’s survival.

Buchanan’s fast day, though intended to foster unity, ended up deepening sectional divisions. Some clergy interpreted it as a call for national repentance over slavery, while others saw it as a condemnation of Republican radicalism, all of which only fanned the flames of discord. Lincoln’s proclamations, by contrast, carried greater institutional weight. His fast day following the Union’s defeat at Bull Run signaled not only a moment of national crisis but also a belief that divine intervention was essential to sustaining the war effort.

Unlike Buchanan’s proclamation, which seemed desperate and ineffectual, Lincoln’s call to prayer was widely embraced, helping to galvanize public support for the Union. More interesting still, by 1863, his proclamations had taken on a more explicitly theological tone, framing the war as divine judgment for the nation’s sins and making national repentance a prerequisite for victory. In light of this, Carwardine argues that these religious appeals were not mere political expedients but crucial in shaping public sentiment, reinforcing the war’s moral stakes, and transforming Lincoln—initially viewed with skepticism by evangelicals—into a leader who increasingly embodied the role of a providential statesman.

Today we often take this view for granted, with Lincoln consistently ranking high on lists of America’s greatest presidents. At the time, however, he was far from an obvious hero for antislavery evangelicals. On the campaign trail, he faced a barrage of baseless accusations, including claims that he was a duelist, a drunkard, and a denier of Christ’s divinity. Even beyond these fabrications, his irregular church attendance and lack of formal membership in any denomination only deepened suspicions among religious voters.

As Carwardine explains, Lincoln was aware of these concerns and quickly learned to keep his religious views guarded, avoiding public declarations that might alienate potential supporters. Yet as the war progressed, evangelicals found their faith in him vindicated. They welcomed his increasingly providential rhetoric alongside his steadfast commitment to preserving the Union.

Clergy reinforced this perception, drawing parallels between Lincoln and biblical figures who had carried out God’s will in times of national crisis. Some likened him to Moses, guiding the people toward liberation, while others saw a resemblance to David, chosen to uphold justice. A Wisconsin senator, James R. Doolittle, captured the depth of this religious devotion in an 1864 statement: “I believe in God. Under Him, and, next to Him, I believe in Abraham Lincoln.”       

Much like white evangelicals, Black Americans initially had deep reservations about Lincoln. But over time, many likewise came to see him as a providential figure. His early statements prioritizing the Union’s survival over the immediate abolition of slavery met with disappointment. And his August 1862 meeting with Black leaders, where he suggested colonization as a solution to racial tensions, provoked outrage. Henry McNeal Turner, a prominent African Methodist Episcopal (AME) minister, denounced him as a “presidential Pharaoh” who courted divine judgment by ignoring the cries of the enslaved.

Yet despite their frustrations, many Black religious leaders maintained faith that God was guiding history. As Lincoln moved toward emancipation, Black leaders began revising their views, interpreting his actions as evidence that he had been appointed God’s agent of deliverance.

By the end of the war, many Black Americans regarded Lincoln as divinely chosen. His 1865 assassination, occurring on Good Friday, only deepened this perception. Both Black and white Americans infused his tragic death with religious meaning. But Carwardine shows how their biblical interpretations were remarkably distinct.

Many white Americans mourned Lincoln as a Christ figure, viewing his death as a form of national atonement. Black Americans more often compared him to Moses. Like the Old Testament leader, Lincoln had brought his people through a “red sea of blood to a Canaan of peace and freedom,” in the words of one Wisconsin judge, only to be stopped short of entering the Promised Land.

Before long, Black churches began displaying his image, from pulpits and altar tables, as a symbol of deliverance and divine justice. A Long Island mass meeting of Black citizens honored him as “God’s appointed instrument to work out our salvation,” while an Illinois AME congregation mourned the loss of “a great deliverer—a real benefactor.”

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In death, then, Lincoln became a sacred figure for Black and white Americans alike. And while he understandably looms large in Righteous Strife, Carwardine broadens the narrative by spotlighting a diverse cast of influential religious figures who shaped the war’s moral and theological battles.

Well-known names like William Lloyd Garrison, Henry Ward Beecher, and Frederick Douglass take center stage, not just as activists but as key players in defining the war’s religious stakes. Alongside them are lesser-known figures like Stephen Higginson Tyng, an Episcopal clergyman and staunch emancipationist, and Matthew Simpson, the influential Methodist bishop who cast the Union cause as a divine mandate. Both played pivotal roles in rallying religious support for Lincoln’s policies.

On the opposing side, Richard Fuller and Nathan Lord defended the Confederacy’s proslavery theology, insisting that slavery was biblically sanctioned and racism God ordained. Meanwhile, figures like William Gannaway Brownlow, a fiery Methodist preacher turned Unionist politician, reveal how religious fervor fueled not only abolitionist activism but also fierce nationalist sentiment. By interweaving voices from across the nation, from abolitionist preachers to proslavery theologians to local clergy from both North and South, Carwardine reveals that the Civil War was waged almost as fiercely in pulpits, prayer meetings, and pews as on battlefields.

At a time when fears of Christian nationalism dominate political discourse, Carwardine’s Righteous Strife offers a powerful reminder that debates over the nation’s religious identity, the church’s role in public life, and the meaning of the gospel in American politics are nothing new. While the battle over slavery has been settled, deeper struggles endure, animated by competing perspectives on how Christians should relate to the nation and what kind of nation (Christian or otherwise) America should embody. Schisms that once resulted from slavery now erupt amid conflicts over race, gender, sexuality, and political ideology, echoing the tensions that split denominations in the antebellum era.

The Christians of Lincoln’s day might not recognize today’s debates, but they would surely recognize the broader shape of our conflict. America’s deepest struggles have always been, at their heart, battles over belief.

Daniel N. Gullotta is a researcher at the Declaration of Independence Center for the Study of American Freedom at the University of Mississippi.