America 1800–1850: Expansion, Industry & the Road to Civil War

The first half of the 19th century transformed the United States from a coastal republic into a continental power—setting forces in motion that would tear it apart.

Territorial Explosion

• 1803 Louisiana Purchase – 828,000 mi² ($15M); doubled size.
• 1819 Adams-Onís Treaty – Florida from Spain.
• 1845 Texas Annexation – Republic → state; triggers Mexican War.
• 1846 Oregon Treaty – 49th parallel to Pacific.
• 1848 Mexican Cession – CA, NV, UT, AZ, NM, CO, WY (Treaty of Guadalupe Hidalgo).

War & Identity

• War of 1812 – Stalemate vs. Britain; forged national symbols (anthem, flag, "Old Ironsides").
• Mexican-American War (1846–48) – Controversial expansion; trained Civil War generals (Grant, Lee, Jackson).

Industrial & Transport Revolution

• Cotton gin (1793) → Cotton Kingdom → slavery entrenched/expanded.
• Erie Canal (1825) – NYC ↔ Great Lakes; 90% freight cost drop.
• Railroads – 9,000 mi by 1850; integrated markets, standardized time.
• Telegraph (1844) – Instant communication; "Victorian Internet."

Westward Migration

• Oregon, California, Santa Fe Trails – 300,000+ pioneers by 1860.
• Mormon Trail (1847) – Utah settlement.
• Gold Rush (1848) – 300K to CA; statehood fast-track.

Politics & Reform

• Jacksonian Democracy (1829–37) – White male suffrage, spoils system, Indian Removal Act (Trail of Tears).
• Manifest Destiny – Divine right to expand; ideological fuel.
• Reform Movements – Abolitionism (Garrison, Douglass), Women's Rights (Seneca Falls 1848), Temperance, Education (Mann), Utopian communities.

Culture

• Literature: Irving, Cooper, Poe, Emerson, Thoreau, Hawthorne, Melville, Whitman.
• Art: Hudson River School (Cole, Church) – wilderness as cathedral.
• Education: Common schools spread; colleges multiply.

By 1850, the map was ~set—but the slavery question in new territories made disunion inevitable. The first half built the house; the second half burned it.