Expansion and Slavery

Why territory mattered

Every time the United States added land, one question arose: would slavery be allowed there? The answer affected the balance of power in the Senate, where each state has two votes, so both free and slave states tried to keep their numbers equal.

Compromises that delayed the crisis

• Missouri Compromise (1820): Missouri entered as a slave state and Maine as a free state, keeping the balance. Slavery was banned in the rest of the Louisiana Purchase north of latitude 36°30'.
• Texas and the Mexican War: Texas won independence from Mexico in 1836 and was annexed in 1845. A dispute over its border led to war with Mexico (1846-48). The Treaty of Guadalupe Hidalgo gave the United States California and most of the present Southwest.
• Wilmot Proviso (1846): proposed banning slavery in any land taken from Mexico. It passed the House but not the Senate, and showed how sharp the divide had become.
• Compromise of 1850: California entered as a free state, and a stricter Fugitive Slave Act required citizens to help return people who had escaped. The Act angered many Northerners.

The compromises break down

The Kansas-Nebraska Act (1854) let settlers in those territories decide on slavery by vote, called popular sovereignty, and effectively cancelled the Missouri line. Fighting broke out in "Bleeding Kansas". The Dred Scott decision (1857) held that Black Americans could not be citizens and that Congress could not bar slavery from the territories. The new Republican Party, formed in 1854, opposed the spread of slavery. John Brown's raid on Harpers Ferry in 1859 deepened Southern fear.

Worked example: reading the Kansas-Nebraska Act

1. The Missouri Compromise banned slavery north of 36°30', which included Kansas.
2. Stephen Douglas proposed that settlers vote on the question instead.
3. That meant slavery might spread into land that had been closed to it for 34 years.
4. Many Northerners saw it as a betrayal of an old agreement, and the Republican Party grew.
5. Pro- and anti-slavery settlers rushed to Kansas, and violence followed.

The key skill: identify what the old rule was, what the new rule changed, and who gained or lost. Here the change helped the expansion of slavery and so split the Democratic and Whig parties.