AP U.S. History · Lesson 1

Expansion and the road to secession

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In the 1840s many Americans believed in manifest destiny. Texas was annexed in 1845, and a treaty with Britain split Oregon at the 49th parallel in 1846. President James K. Polk sent troops into land claimed by both the United States and Mexico, and after a clash there Congress declared war in 1846. In the Treaty of Guadalupe Hidalgo (1848) Mexico gave up the Mexican Cession, and the 1849 gold rush pulled settlers to California. Mexicans who stayed were promised citizenship and property rights, but many lost their land in later disputes.

The new land reopened the slavery question. The Wilmot Proviso (1846) would have banned slavery there and never passed the Senate. The Compromise of 1850 admitted California as a free state, let popular sovereignty decide in Utah and New Mexico, ended the slave trade in Washington, D.C., and passed a harsh Fugitive Slave Act, which turned many Northerners against slavery. Harriet Beecher Stowe's novel Uncle Tom's Cabin (1852) spread that anger.

The Kansas-Nebraska Act (1854) repealed the Missouri Compromise line, and fighting broke out in Kansas. The Whig Party collapsed, and the new Republican Party formed to stop slavery's spread. In Dred Scott v. Sandford (1857) the Supreme Court ruled that Black Americans were not citizens and that Congress could not ban slavery in the territories. John Brown's raid on Harpers Ferry (1859) deepened Southern fears.

In 1860 the Democrats split, and Lincoln won with almost no Southern votes. Seven Deep South states seceded before he took office, and four more left after the war began at Fort Sumter in April 1861. The secession declarations that several states issued, such as South Carolina's and Mississippi's, named the defense of slavery as a central reason.

From compromise to crisis
YearEventEffect on the slavery question
1846Wilmot ProvisoVotes split by section, not party
1850Compromise of 1850California free; popular sovereignty in Utah and New Mexico; stronger Fugitive Slave Act
1854Kansas-Nebraska ActRepealed the 36°30′ line; Bleeding Kansas; the Republican Party formed
1857Dred Scott v. SandfordCongress could not ban slavery in the territories
1860Lincoln's electionDeep South states began to secede

Trap Republicans were not abolitionists

In 1860 the Republican Party promised to stop slavery from spreading into the territories, not to end it in the states where it already existed. Lincoln said he had no power to touch slavery in those states. Southern leaders seceded anyway, because they saw a party hostile to slavery winning the presidency without them.

Worked example Easy

Which law turned many Northerners against slavery by requiring citizens to help capture people who had escaped from it?

  1. The Kansas-Nebraska Act of 1854
  2. The Fugitive Slave Act of 1850Answer
  3. The Homestead Act of 1862
  4. The Wilmot Proviso of 1846

How to solve it

  1. The clue is a duty placed on ordinary citizens to help catch people who escaped slavery.
  2. That duty came from the Fugitive Slave Act, part of the Compromise of 1850.

Why each choice is right or wrong

  • A. Incorrect. The Kansas-Nebraska Act opened territories to slavery by popular sovereignty; it did not deal with capturing people who escaped.
  • B. Correct. The Fugitive Slave Act, part of the Compromise of 1850, required citizens to help catch people who escaped slavery and denied the accused a jury trial.
  • C. Incorrect. The Homestead Act gave western land to settlers and had nothing to do with escaped slaves.
  • D. Incorrect. The Wilmot Proviso proposed banning slavery in land won from Mexico and never became law.

Explain Explain it

Task verbs: explain, analyze

Causation questions about the 1850s reward a chain: a development, what it changed, and why that pushed the sections apart. For example, the Kansas-Nebraska Act repealed a line Northerners thought was settled, so many Northern Whigs and Democrats left their parties, and the Republican Party grew from that anger.

When a source is part of the story, ask what it was meant to do. A secession declaration is written to justify leaving the Union, so it tells you what its authors wanted others to believe was at stake.

Worked example Medium

Why did the Kansas-Nebraska Act of 1854 anger many Northerners?

  1. It opened land north of the 36°30′ line to slaveryAnswer
  2. It admitted California to the Union as a slave state
  3. It banned slavery in all the western territories
  4. It allowed the federal government to buy and free enslaved people

How to solve it

  1. Recall what the act did: it used popular sovereignty in Kansas and Nebraska.
  2. Both territories lay north of 36°30′, where slavery had been banned since 1820.
  3. Undoing that ban is what angered the North.

Why each choice is right or wrong

  • A. Correct. By letting settlers decide, the act repealed the Missouri Compromise ban on slavery north of 36°30′, land Northerners thought had been closed to slavery for good.
  • B. Incorrect. California entered as a free state in 1850, and the Kansas-Nebraska Act did not concern California.
  • C. Incorrect. The act did the opposite of a ban: it let settlers choose slavery if they voted for it.
  • D. Incorrect. The act had no plan to buy and free enslaved people; it organized two territories.

Explain Your turn

Explain how the war with Mexico (1846 to 1848) made conflict over slavery worse in the years that followed.

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A full answer does this

  • Says the war brought the United States large new lands
  • Explains how fights over slavery in those lands sharpened the conflict

Model answer

By winning the war, the United States gained the Mexican Cession, including California and the Southwest. Whether slavery could spread into that land became a bitter fight: the Wilmot Proviso to ban it split Congress by section, and the Compromise of 1850 only patched the dispute with a harsh Fugitive Slave Act that angered the North.

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