U.S. Expansion in the 1840s: Treaties, Manifest Destiny, and Conflicts

Treaty of Guadalupe Hidalgo

The 1848 treaty ending the Mexican-American War; Mexico ceded the Mexican Cession to the U.S., the Rio Grande became the Texas border, and the U.S. paid $15 million.

Texas and Oregon

Territories central to Manifest Destiny; Texas was annexed in 1845, Oregon was jointly occupied with Britain until the Oregon Treaty of 1846.

Manifest Destiny

The belief that the U.S. was destined to expand across the continent from the Atlantic to the Pacific, driving expansion in the 1840s.

James K. Polk

President (1845-1849) who aggressively pursued Manifest Destiny, oversaw annexation of Texas, settlement of Oregon, and the Mexican-American War.

U.S.-British Relations in the 1830s

Generally peaceful but tense over boundaries (Oregon, Maine), trade issues, and Canadian rebellions near the border.

Sources of Tension with Britain

Border disputes (Oregon boundary, Aroostook War), trade competition, and American sympathy for Canadian rebels.

Why Texas Was Admitted

Texas was admitted in 1845 due to American expansionist pressure, fear Britain might influence Texas, and Polk's election signaling pro-annexation support.

How the Oregon Boundary Was Resolved

The Oregon Treaty (1846) established the 49th parallel as the U.S.-British boundary, peacefully dividing the Oregon Territory.

Direct Cause of the Mexican-American War

Mexican and American troops clashed in disputed territory between the Nueces River and the Rio Grande in 1846.

Polk's Real Goal in the War

Acquiring California and New Mexico to complete U.S. expansion to the Pacific.

Californios

Spanish-speaking Mexican residents of California before U.S. annexation; many lost land after the war.

Wilmot Proviso

A failed 1846 proposal banning slavery in any territory gained from Mexico, increasing sectional conflict.

Domestic Effects of the Mexican-American War

Increased U.S. territory, intensified the slavery debate, military training for future Civil War leaders, and political tension between North and South.

Manifest Destiny Achieved in the 1840s

U.S. annexed Texas, settled Oregon, and gained the Mexican Cession after the Mexican-American War.

Winfield Scott

U.S. general who captured Mexico City in 1847, helping win the war; later became a presidential candidate.

John Tyler

President before Polk who pushed through the annexation of Texas in his final days in office.

Aroostook War

A boundary dispute between U.S. (Maine) and Britain (Canada) in the 1830s; ended with the Webster-Ashburton Treaty.

Nicholas Trist

U.S. diplomat who negotiated the Treaty of Guadalupe Hidalgo despite Polk ordering him home.

Timber Country

A term often referring to forested frontier areas where land disputes and lumber conflicts (like in the Aroostook region) occurred.