Causes of the Civil War

Why This Matters

The Civil War wasn't an inevitable explosion—it was the result of decades of mounting pressure along specific fault lines: sectional economic interests, constitutional debates over federal power, and the moral crisis of slavery. You're being tested not just on what happened, but on how these causes interconnected and escalated. The AP exam loves asking you to trace how a single compromise or court decision rippled outward, making conflict more likely.

Think of the antebellum period as a pressure cooker with multiple release valves—the Missouri Compromise, the Compromise of 1850, popular sovereignty—each one failing in turn. The key insight is that every "solution" to the slavery question actually deepened the crisis by exposing how fundamentally incompatible the Northern and Southern visions for America had become. Don't just memorize dates and names—know what principle each event illustrates and how it connects to the ultimate breakdown of the Union.

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The Slavery Question: America's Original Sin

At its core, the sectional crisis was about whether slavery would survive, expand, or die. Every political battle, economic argument, and constitutional debate ultimately circled back to this fundamental question about human bondage and its future in the republic.

Slavery and Its Expansion

• Cotton economy created Southern dependence on enslaved labor—by 1860, nearly 4 million enslaved people generated the wealth that made the South politically powerful
• Territorial expansion forced the issue into national politics repeatedly, as each new state threatened to tip the balance of power in Congress
• Abolitionist movement transformed slavery from a political question into a moral crusade, making compromise increasingly difficult for Northern politicians

Dred Scott Decision (1857)

• Supreme Court ruled enslaved people were property, not citizens—Chief Justice Taney declared Black Americans had "no rights which the white man was bound to respect"
• Congress lacked authority to ban slavery in territories, effectively declaring the Missouri Compromise unconstitutional and opening all western lands to slavery
• Radicalized Northern opinion by suggesting slavery could spread anywhere, even into free states, through the protection of property rights

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Failed Compromises: Buying Time, Not Peace

Each major compromise attempted to balance free and slave state interests, but the underlying conflict over slavery's morality and expansion made lasting peace impossible. These legislative band-aids reveal how politicians prioritized Union over resolution.

Missouri Compromise (1820)

• Established the 36°30' line dividing future slave and free territories, creating a geographic formula for managing expansion
• Admitted Missouri (slave) and Maine (free) to maintain Senate balance—the first explicit acknowledgment that sectional power required careful management
• Set the precedent that slavery's expansion was a national political question, not just a state matter, which would haunt future debates

Compromise of 1850

• California admitted as a free state, tipping the Senate balance and alarming Southern leaders about their declining political power
• Fugitive Slave Act strengthened federal enforcement of slave-catching, forcing Northerners to participate in slavery's maintenance and radicalizing moderate opinion
• Popular sovereignty introduced for New Mexico and Utah territories, abandoning the Missouri Compromise's geographic solution for democratic choice

Kansas-Nebraska Act (1854)

• Repealed the Missouri Compromise line by allowing popular sovereignty in territories north of 36°30', reopening supposedly settled territory to slavery
• "Bleeding Kansas" violence erupted as pro-slavery and free-soil settlers flooded the territory, turning democratic choice into armed conflict
• Destroyed the Whig Party and created the Republican Party, fundamentally realigning American politics around the slavery question

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States' Rights and Constitutional Crisis

The states' rights argument provided constitutional cover for protecting slavery, but it also reflected genuine disagreement about the nature of the Union. Understanding this debate helps explain why Southerners framed secession as legally justified.

States' Rights vs. Federal Authority

• Nullification theory held that states could reject federal laws they deemed unconstitutional—South Carolina had tested this during the 1832 Tariff Crisis
• Compact theory of Union argued states had voluntarily joined and could voluntarily leave, making secession a constitutional right rather than rebellion
• Federal enforcement of Fugitive Slave Act ironically required Southerners to support strong federal power when it protected slavery, exposing the selective nature of states' rights arguments

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Economic Sectionalism: Two Americas

The North and South developed fundamentally different economic systems that required different labor arrangements, trade policies, and visions for western expansion. These material interests reinforced ideological divisions.

Economic Differences Between North and South

• Industrial North relied on wage labor and protective tariffs—factory owners wanted high tariffs to protect American manufacturing from British competition
• Agricultural South depended on slave labor and free trade—planters wanted low tariffs to reduce costs on imported goods and maintain European markets for cotton
• Western expansion meant different things to each section: free soil for Northern farmers and workers vs. new slave territory for Southern planters seeking fresh land

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The Breaking Point: Events of the 1850s

The final decade before war saw a rapid escalation as political compromises failed, violence erupted, and radical actions on both sides made reconciliation impossible. These events transformed theoretical conflict into imminent crisis.

John Brown's Raid on Harpers Ferry (1859)

• Armed raid on federal arsenal aimed to seize weapons and spark a massive slave uprising across the South
• Brown's execution made him a martyr in the North—church bells tolled, and intellectuals like Emerson praised him as a saint
• Terrified Southern whites who saw the raid as proof that abolitionists would use violence to destroy slavery, making them view all Northern criticism as existential threat

Election of Abraham Lincoln (1860)

• Won without a single Southern electoral vote, proving the South had lost control of the federal government permanently
• Republican platform opposed slavery's expansion, not abolition—but Southerners saw no meaningful distinction
• Triggered secession within weeks of the election, as seven Deep South states left before Lincoln even took office

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Quick Reference Table

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Self-Check Questions

1. How did the Kansas-Nebraska Act undermine the Missouri Compromise, and why did this shift from geographic division to popular sovereignty increase violence?

2. Compare the Compromise of 1850 and the Missouri Compromise—what problem-solving approach did each take, and why did neither provide a lasting solution?

3. Which two events most directly convinced Southern whites that abolitionists posed an existential threat to their society? What evidence would you use to support this in an FRQ?

4. How did the Dred Scott decision change the legal landscape for slavery's expansion, and why did it radicalize Northern opinion even among people who weren't abolitionists?

5. Explain how economic differences between North and South reinforced the political conflict over slavery—could sectionalism have existed without the slavery question at its center?