Civil War Causes: Why America Went to War with Itself
Grade 5 · Social Studies · Study Guide
Explore the deep divisions over slavery, states' rights, and economics that split the United States and led to the Civil War.
The American Civil War (1861–1865) was the deadliest conflict in American history, with over 620,000 soldiers killed. It was fought between the Northern states (the Union) and eleven Southern states that seceded (broke away) to form the Confederate States of America. Understanding why the war happened requires looking at decades of growing tension between the North and South.
The single most important cause of the Civil War was slavery. By 1860, there were about four million enslaved African Americans in the United States — almost all of them in the South. The entire Southern economy was built on enslaved labor, particularly on huge cotton and tobacco plantations. The North, by contrast, had an industrial economy that didn't rely on enslaved people. As new territories were added to the country, a fierce political battle erupted over whether slavery would be allowed to spread westward. Compromises like the Missouri Compromise (1820) and the Compromise of 1850 tried to keep peace, but they only postponed the crisis.
Other contributing causes included states' rights — the argument that individual states had the right to ignore or override federal laws they disagreed with. Southern leaders argued that states had the right to leave the Union (secession) if the federal government threatened their way of life. The election of Abraham Lincoln in 1860 was the final trigger. Though Lincoln had promised not to abolish slavery where it already existed, Southern states feared he would eventually end it. Within months of his election, seven Southern states had seceded and the Confederacy was formed. The first shots of the Civil War were fired at Fort Sumter, South Carolina, in April 1861.
| Category | North (Union) | South (Confederacy) |
|---|---|---|
| Economy | Industrial — factories, manufacturing | Agricultural — cotton and tobacco plantations |
| Labor | Paid free workers (mostly) | Enslaved African Americans (about 4 million) |
| Population | ~22 million | ~9 million (including ~3.5 million enslaved) |
| Railroads | Over 22,000 miles of track | About 9,000 miles of track |
| View on slavery | Growing antislavery movement; many wanted to limit its spread | Defended slavery as essential to economy and way of life |
| Year | Event | Significance |
|---|---|---|
| 1820 | Missouri Compromise | Temporarily balanced slave and free states; drew a line across new territory |
| 1850 | Compromise of 1850 | Admitted California as free; included Fugitive Slave Act |
| 1852 | Uncle Tom's Cabin published | Harriet Beecher Stowe's novel turned many Northerners against slavery |
| 1857 | Dred Scott Decision | Supreme Court ruled enslaved people were property, not citizens; outraged the North |
| 1860 | Lincoln elected President | Southern states feared he would end slavery; secession began |
| April 1861 | Attack on Fort Sumter | Confederate attack on a Union fort; Civil War officially began |
Key terms
- Secession
- When a state or group of states breaks away from the larger nation; eleven Southern states seceded to form the Confederacy.
- Confederacy
- The Confederate States of America — eleven Southern states that seceded from the Union in 1860–1861.
- Union
- The Northern states that fought to preserve the United States during the Civil War.
- Slavery
- The practice of holding people as property, forcing them to work without pay; the central cause of the Civil War.
- States' rights
- The argument that individual states have the right to govern themselves and can challenge federal authority.
- Missouri Compromise
- An 1820 agreement that allowed Missouri to enter as a slave state and Maine as a free state, maintaining a balance in Congress.
- Abolitionist
- A person who wanted to abolish (end) slavery completely.
Practice questions
What was the most important single cause of the American Civil War?
- Tariffs and trade policy
- Slavery
- Immigration
- Railroad disputes
Show answer
Answer: Slavery
The eleven Southern states that broke away from the United States formed the __________ States of America.
Show answer
Answer: Confederate
The Missouri Compromise permanently solved the conflict over slavery in new territories.
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Answer: False
The Civil War officially began when Confederate forces attacked which location?
- Richmond, Virginia
- Gettysburg, Pennsylvania
- Fort Sumter, South Carolina
- Washington D.C.
Show answer
Answer: Fort Sumter, South Carolina
Abraham Lincoln's election in 1860 alarmed Southern states who feared he would eventually end slavery.
Show answer
Answer: True
Fun facts
- Harriet Beecher Stowe's anti-slavery novel Uncle Tom's Cabin (1852) sold 300,000 copies in its first year — when Abraham Lincoln met her, he reportedly said, 'So you are the little woman who wrote the book that started this great war.'
- The Dred Scott Supreme Court decision of 1857, which ruled that enslaved people were property and had no rights as citizens, outraged people in the North and further inflamed tensions between the sections.
- More Americans died in the Civil War than in any other conflict in U.S. history — more than in both World Wars combined.
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