Chapter 17

Manifest Destiny and Its Legacy

1841–1848

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The Accession of "Tyler Too"

President William Henry Harrison died just one month into his term in 1841, elevating Vice President John Tyler to the presidency — the first time a vice president assumed office after a president's death.

Tyler, a former Democrat only nominally a Whig, clashed repeatedly with Whig leaders in Congress, vetoing their bank and tariff bills and becoming a president without a party, nicknamed "His Accidency."

The Westward Movement and Oregon

A replica covered wagon representing the thousands that carried settlers along the Oregon Trail in the 1840s. Public domain (CC BY), via Wikimedia Commons.
A replica covered wagon representing the thousands that carried settlers along the Oregon Trail in the 1840s. Public domain (CC BY), via Wikimedia Commons.

Thousands of American pioneers braved the grueling Oregon Trail in the 1840s, seeking fertile farmland in the Pacific Northwest. The United States and Britain jointly occupied the Oregon Country until growing American settlement forced a resolution.

Expansionists chanted "Fifty-Four Forty or Fight!", demanding all of Oregon up to the Alaska border, but in 1846 the two nations peacefully compromised on the 49th parallel as the boundary, avoiding war with Britain.

The Mormon Trek and the Texas Question

Fleeing persecution, Brigham Young led the Mormons on a grueling trek to the Great Salt Lake basin in Utah in 1846-47, where they built an isolated, thriving community.

Meanwhile, the independent Republic of Texas, having won independence from Mexico in 1836, still sought annexation to the United States. Northern politicians had long blocked the move, fearing it would add another slave state and provoke war with Mexico, which still claimed Texas as its own territory.

Polk and Manifest Destiny

"American Progress," an 1872 allegorical painting depicting westward expansion, often used to illustrate the idea of Manifest Destiny. Painting by John Gast. Public domain, via Wikimedia Commons.
"American Progress," an 1872 allegorical painting depicting westward expansion, often used to illustrate the idea of Manifest Destiny. Painting by John Gast. Public domain, via Wikimedia Commons.

The doctrine of Manifest Destiny — the belief that the United States was fated by God to expand across the continent — swept the nation in the 1840s, fueling support for aggressive territorial growth.

Dark-horse candidate James K. Polk won the presidency in 1844 on an expansionist platform, promising to annex both Texas and Oregon. Congress annexed Texas just before Polk took office in 1845, angering Mexico, which severed diplomatic relations.

Polk then sent envoy John Slidell to Mexico City in a failed attempt to buy California and settle the Texas border dispute, while ordering General Zachary Taylor's troops into the disputed territory between the Nueces River and the Rio Grande.

President James K. Polk, whose expansionist administration oversaw the annexation of Texas, the Oregon settlement, and the Mexican-American War. Photograph by Mathew Brady. Public domain, via Wikimedia Commons.
President James K. Polk, whose expansionist administration oversaw the annexation of Texas, the Oregon settlement, and the Mexican-American War. Photograph by Mathew Brady. Public domain, via Wikimedia Commons.

The Mexican-American War

General Zachary Taylor, whose victories in the Mexican-American War made him a national hero and later president. Portrait by George P. A. Healy. Public domain, via Wikimedia Commons.
General Zachary Taylor, whose victories in the Mexican-American War made him a national hero and later president. Portrait by George P. A. Healy. Public domain, via Wikimedia Commons.

After a clash between American and Mexican troops in the disputed border zone, Polk declared that Mexico had "shed American blood upon American soil," and Congress declared war in 1846 — though many, including a young congressman named Abraham Lincoln, doubted Polk's account.

American forces under Zachary Taylor won victories in northern Mexico, while another force under Winfield Scott captured Mexico City itself after storming the fortress of Chapultepec in 1847, effectively ending Mexican resistance.

Simultaneously, American forces under John C. Frémont and Stephen Kearny seized California with little resistance, aided by American settlers who had already declared the short-lived "Bear Flag Republic."

The storming of Chapultepec castle in 1847, the decisive battle that opened the way to Mexico City. Painting by James Walker. Public domain, via Wikimedia Commons.
The storming of Chapultepec castle in 1847, the decisive battle that opened the way to Mexico City. Painting by James Walker. Public domain, via Wikimedia Commons.

The Treaty of Guadalupe Hidalgo

A map of the Mexican Cession of 1848, the vast territory ceded by Mexico to the United States after the Mexican-American War. Public domain (CC BY), via Wikimedia Commons.
A map of the Mexican Cession of 1848, the vast territory ceded by Mexico to the United States after the Mexican-American War. Public domain (CC BY), via Wikimedia Commons.

The war ended with the Treaty of Guadalupe Hidalgo (1848), in which Mexico ceded the vast Mexican Cession — including California and the future Southwest — to the United States for $15 million, while recognizing the Rio Grande as the Texas border.

Congressman David Wilmot had proposed the Wilmot Proviso in 1846, seeking to ban slavery in any territory won from Mexico; though it repeatedly passed the House, it failed in the Senate, but it inflamed sectional tensions over whether the new lands would be slave or free.

The California Gold Rush

California gold miners using a "long tom" sluice to pan for gold during the Gold Rush. Photograph by George H. Johnson. Public domain, via Wikimedia Commons.
California gold miners using a "long tom" sluice to pan for gold during the Gold Rush. Photograph by George H. Johnson. Public domain, via Wikimedia Commons.

Gold was discovered at Sutter's Mill, California, in January 1848, just days before the Treaty of Guadalupe Hidalgo was signed. News of the strike triggered the California Gold Rush, drawing tens of thousands of "forty-niners" from across the country and around the world.

California's population exploded almost overnight, forcing the territory to draft a state constitution and apply for admission to the Union — as a free state — reigniting the explosive question of slavery's expansion that would soon demand the Compromise of 1850.