The Kansas-Nebraska Act sparked violence that foreshadowed the Civil War

US westward expansion—and the status of slavery in the new territories—was a major cause of the American Civil War

The addition of new western lands forced the nation to confront whether slavery would spread beyond the South. Each debate over the admission of a new state sharpened the divide between free and slaveholding regions.

The Lincoln-Douglas debates sharpened the national divide over slavery

In 1858, Abraham Lincoln and Senator Stephen Douglas debated while competing for an Illinois Senate seat. Their seven debates, reprinted nationwide, brought the question of slavery to the forefront—further polarizing the country and propelling Lincoln to national prominence.

The Compromise of 1850 tried to settle disputes over land gained from Mexico

Territory acquired in the Mexican-American War reignited fierce debates over slavery’s expansion. The Compromise of 1850 aimed to ease tensions by admitting California as a free state and letting other territories decide the issue—but the compromise ultimately failed and helped pave the way to the Civil War.

Congress descended into fistfights, duels, and violence before the Civil War

In the decades before the Civil War, members of the United States Congress carried weapons, assaulted colleagues, and, in one case, a congressman killed another in a duel. The violence was driven largely by sectional conflict over slavery and foreshadowed the nation's descent into war.

View animated battle maps from every major skirmish of the American Civil War.

Abraham Lincoln received only 40% of the popular vote in the 1860 election, highlighting the deep divisions in the country on the eve of the Civil War.

The Missouri Compromise temporarily eased tensions over slavery's expansion

Passed in 1820, the Missouri Compromise admitted Missouri as a slave state and Maine as a free state—maintaining the fragile balance between proslavery and antislavery states in Congress. It also banned slavery north of latitude 36°30′.

Abraham Lincoln's victory in 1860 sparked Southern secession—even before his inauguration

Abraham Lincoln's election on an antislavery expansion platform convinced many Southerners that their way of life was under threat. Within three months, seven states seceded from the Union—forming the Confederacy—before Lincoln took office in March 1861.

Abraham Lincoln's election in 1860 triggered a cascade of Southern secessions and the formation of the Confederacy, culminating in the Confederate attack on Fort Sumter in Charleston, South Carolina.

Future President Abraham Lincoln challenged Polk’s justification for war with Mexico

As a freshman congressman, Abraham Lincoln introduced the “Spot Resolutions,” demanding President Polk prove that Mexico had attacked on US soil. This constituted Lincoln’s first major political stand and highlighted growing dissent over the war.

Bills passed during the Civil War shaped postwar America

Despite the war with the South, Congress passed transformative laws like the Homestead Act and the Morrill Land-Grant College Act, which encouraged westward settlement and expanded higher education.

President Polk deliberately provoked war with Mexico

After Mexico refused to sell California and New Mexico, President James K. Polk ordered US troops into disputed territory between the Nueces River and the Rio Grande—knowing it would likely spark a conflict. When fighting broke out, he used it to justify declaring war.

Was the Civil War really about states' rights?

The Civil War was fought over slavery, and Confederate leaders and supporters admitted as much in the build-up to the war and after. But later on, after the South's defeat, the lie of the Lost Cause was pushed—and it persists to this day. This four-minute video details the story of the Lost Cause, "state's rights", Confederate monuments, and the machinations behind them.

According to Confederate leaders, the defense of slavery was the primary reason for secession.

11 states formed the Confederacy, with 2 others claiming allegiance

Between December 1860 and June 1861, 11 Southern states officially seceded to form the Confederacy. Pro-Confederate factions in Missouri and Kentucky also declared secession, but both states remained largely under Union control throughout the war.

Learn how Mexico’s anti-slavery stance shaped the US–Texas conflict

Historian Alice Baumgartner explores how Mexico’s abolition of slavery clashed with Anglo settlers' ambitions in Texas. The episode reveals how enslaved people fled south to freedom, reshaping the politics that led to Texas independence and the Mexican-American War.

The Dred Scott decision denied citizenship to people of African descent

In 1857, the Supreme Court ruled in Dred Scott v. Sandford that Black Americans could not be US citizens. The decision heightened an already brewing conflict and became a key factor in pushing the nation toward civil war.

The abolitionist movement long predated the Civil War

Beginning in the late 18th century, abolitionists like Frederick Douglass, William Lloyd Garrison, and Sojourner Truth campaigned through newspapers, lectures, and political action to end slavery.

Congress's Wade-Davis Bill demanded harsher terms for Southern reentry

Passed in 1864, the Wade-Davis Bill required 50% of white male voters to swear loyalty and guarantee emancipation before readmission. Lincoln pocket-vetoed it, rejecting Congress's stricter approach.

Southern race riots in 1866 galvanized support for more radical Reconstruction

In 1866, white mobs in Memphis and New Orleans killed dozens of Black residents and burned Black neighborhoods. The massacres horrified Northerners, convincing Congress that stronger federal action was needed to protect freedpeople's rights and enforce Reconstruction.

Hear how the world reacted to the American Civil War

European nations closely watched the Civil War for its economic and political consequences. Some European nations quietly engaged diplomatically with the Confederacy but withheld recognition. When the Union made slavery's abolition a central cause, European public opinion turned sharply against the South.

In the midst of the Civil War, Lincoln rapidly expanded presidential power

Abraham Lincoln suspended habeas corpus, expanded the army without congressional approval, and issued the Emancipation Proclamation—despite likely lacking authority to unilaterally alter national slave law. His actions set precedents for expanded presidential power in wartime.

The Civil War was the deadliest conflict in American history

Between 1861 and 1865, an estimated 620,000 to 750,000 soldiers died from battle and disease—more than in all other US wars combined.

White supremacist groups like the Ku Klux Klan emerged to undermine Reconstruction

Founded in 1865 by former Confederate officers in Tennessee, the Ku Klux Klan used terror, murder, and intimidation to suppress Black political power and restore white Democratic control across the postwar South.

Read an annotated 1866 essay by abolitionist Frederick Douglass, where he laid out his vision for reshaping America after the Civil War.

Silent film star Buster Keaton tried to turn the Civil War into a comedy with the 1926 film 'The General,' which was panned by critics for its pro-Confederate themes and tone-deaf treatment of war.

Lincoln's original reconstruction vision prioritized reconciliation

Proposed in 1863, Lincoln's Ten Percent Plan offered lenient readmission for Southern states once 10% of voters pledged loyalty and ended slavery. It was adopted in a few Union-occupied areas but was only partially implemented before his assassination in 1865.

The Civil War permanently strengthened federal power

The Civil War expanded federal power through emancipation, national military mobilization, and postwar civil rights laws, permanently strengthening the national government and shifting the balance of authority away from the states.

Abolitionists shaped American history from the Revolution to the Civil War

Abolitionists of all backgrounds organized against slavery from the founding era onward. Historian Manisha Sinha argues that their decades of activism fundamentally shaped American democracy and made emancipation possible.

Where was the Civil War fought?

The Civil War is commonly described as a war between northern and southern US states, but where was the war actually fought? Watch this interactive map and timeline to see who fought who and when. Click on specific battles to learn more about each fight.

American annexation of Texas eventually sparked war with Mexico

After Texas won independence from Mexico in 1836, the US annexed it in 1845—despite Mexico’s refusal to recognize Texas as separate. That annexation, combined with a heated border dispute, triggered the Mexican-American War the following year.

Support for slavery helped drive Texas to revolt against Mexico

Mexico abolished slavery in 1829, but many Anglo-American settlers in Texas brought enslaved people and refused to comply. Their desire to preserve slavery was a major factor in Texas’s 1836 rebellion and independence from Mexico.

How the US took half of Mexico

In just two years, the United States redrew the map of North America. Sparked by border disputes in Texas and fueled by President James Polk’s drive for expansion, the Mexican–American War (1846–1848) reshaped both nations.

The disputed 1876 Presidential election accelerated the end of Reconstruction

The 1876 election between Rutherford B. Hayes and Samuel J. Tilden ended in a deadlock over contested Southern votes. To resolve the crisis, Democrats accepted Hayes's presidency in exchange for the withdrawal of federal troops—formally ending Reconstruction.

The Civil War introduced many technological advances to both society and warfare.

The Civil War turned the Continental Divide into an American symbol of identity

Historians argue that the boundary only became a celebrated American symbol in the 1860s, when Civil War-era leaders promoted a west-east geographic divide to replace the devastating north-south political divide, and that the term's use spiked after the transcontinental railroad crossed it in 1868.

Radical Reconstruction began in response to the lenient policies of Andrew Johnson

In 1867, Congress passed the Reconstruction Acts—overriding Johnson's vetoes—placing the South under military rule and requiring new state constitutions, Black male suffrage, and ratification of the 14th Amendment before readmission.

The US Army massacred close to 300 Lakota men, women, and children at Wounded Knee in 1890

Fearing the Ghost Dance—a spiritual movement spreading across starving reservations—the Army surrounded a Lakota encampment at Wounded Knee Creek, South Dakota. When a shot was fired during an attempted disarmament, it sparked chaos, and soldiers killed nearly 300 people.

The Kent State massacre sparked a nationwide student strike

In 1970, the Ohio National Guard opened fire on Kent State University students—peacefully protesting the Vietnam War—and killed four. The tragedy led to more widespread nationwide protests, shutting down more than 200 colleges and universities. The event led to a Pulitzer Prize-winning photo of a slain and grieving student.

US troops committed widespread atrocities during the Mexican-American War

American volunteer regiments frequently looted towns, raped civilians, and executed prisoners—especially in occupied northern Mexico. Historians have documented how racial hatred and impunity fueled war crimes that were rarely punished by military leadership.

The Emancipation Proclamation shifted the purpose of the war for the Union

Issued on Jan. 1, 1863, the Emancipation Proclamation declared enslaved people in Confederate-held territory free, redefining the Union's cause from merely preserving the nation to abolishing slavery.

What led to the Vietnam War?

On the heels of gaining independence from colonizers, why did Vietnam fracture and begin its internal battle? Though the war took root during an independence movement against French colonial rule, it evolved into a Cold War confrontation with international support. This article explains six events that led to the conflict between North and South Vietnam.

Why Kansas is giving away cheap land

In Lincoln, Kansas, a housing renaissance is underway, driven by affordable real estate prices and a lower cost of living, in stark contrast to high-priced urban centers. Bradley Roberts, who previously lived in San Francisco, moved to Lincoln and...

Thoreau's 'Civil Disobedience' was largely a protest against the Mexican-American War

Henry David Thoreau refused to pay taxes that funded what he saw as an unjust war waged to expand slavery. His act of protest inspired his famous essay "Civil Disobedience," a foundational text for nonviolent resistance.

Southern states enacted voting restrictions aimed at circumventing Reconstruction

After 1877, former Confederate states passed poll taxes, literacy tests, property requirements, and grandfather clauses to disenfranchise Black voters—restrictions that remained in place for nearly a century until the Voting Rights Act of 1965.

Mexico admired Lincoln for opposing the war and supporting Mexican sovereignty

As a congressman, Abraham Lincoln condemned the Mexican-American War as unjust. Years later, as president, he backed Mexico’s fight against French occupation. His principled stance earned enduring respect and monuments across Mexico.

Listen to a widely lauded historical fiction podcast about the manhunt and power struggle that gripped the US after President Abraham Lincoln's assassination.

Manifest destiny fueled US aggression against Mexico

The belief that the United States had a divine right to expand westward—known as manifest destiny—justified President Polk’s push for territorial conquest. It shaped public support for the Mexican-American War and framed the invasion as national destiny.

Listen to firsthand accounts of how Black Americans fought to end slavery and shape Reconstruction

This podcast explores the actions of Black Americans who fought for freedom before, during, and after the Civil War—highlighting their key role in abolition and the Reconstruction era.

The election of 1868 cemented power and support for Radical Reconstruction

In the first presidential election after the Civil War, Republican Ulysses S. Grant defeated Democrat Horatio Seymour. President Andrew Johnson, deeply unpopular with both parties, was denied renomination. Grant's victory reflected Northern support for Reconstruction.