Overview
This lecture explores the causes, major events, and lasting consequences of the Mexican-American War (1846–1848), emphasizing its controversial nature and profound effects on U.S. history.
Origins of the Mexican-American War
- The war began after the U.S. annexed Texas, leading Mexico to break off diplomatic relations.
- President Polk sought to acquire California and New Mexico and deliberately provoked hostilities by sending U.S. troops to disputed territory.
- The Thornton Affair, where Mexican troops killed 11 Americans, served as the pretext for war.
- On May 13, 1846, Congress declared war, authorizing over 50,000 troops.
Regional Reactions and Political Controversy
- The South was highly supportive of the war, supplying many volunteers (e.g., Tennessee became the "Volunteer State").
- The North was less enthusiastic and saw the war as Polk’s attempt to expand slavery.
- Figures like John Quincy Adams and Abraham Lincoln criticized the war’s legitimacy and motives.
U.S. and Mexican Advantages
- U.S. advantages: larger population (20 million vs. Mexico’s 7 million), stronger economy, better-trained and equipped military.
- Mexico’s main advantage was fighting on home territory.
Campaigns in California and New Mexico
- John C. Fremont led a covert mission to seize California, establishing the short-lived Bear Flag Republic.
- U.S. forces quickly overran California and New Mexico with minimal resistance.
Battles in Northern Mexico and Leadership Changes
- General Zachary Taylor achieved early victories, increasing his fame and political threat to Polk.
- Antonio López de Santa Anna returned from exile, led Mexican forces, but was defeated at Buena Vista.
- Polk shifted command to Winfield Scott for political reasons.
Scott’s Campaign and the Fall of Mexico City
- Winfield Scott led a successful amphibious landing at Veracruz, then marched on Mexico City.
- Key battles at Sierra Gordo, Puebla, and Chapultepec led to the fall of Mexico City in September 1847.
Treaty of Guadalupe Hidalgo and Immediate Aftermath
- The Treaty ended the war in 1848, with Mexico ceding over 525,000 square miles (the Mexican Cession) for $15 million.
- Expansionists wanted even more territory, but the treaty limited the acquisition to current U.S. Southwest states.
Lasting Legacies of the War
- First time the U.S. defeated and occupied another country.
- Most lethal war for U.S. soldiers by death rate.
- Widely regarded as a war of conquest and a source of national shame; no national memorial exists.
- Trained future Civil War leaders and tactics, including Ulysses S. Grant and Robert E. Lee.
- The new territories reignited the national debate over slavery, fueling sectional tensions leading to the Civil War.
Key Terms & Definitions
- Mexican-American War — Armed conflict between the U.S. and Mexico from 1846 to 1848.
- Annexation — The formal addition of territory, as in the U.S. annexation of Texas.
- Thornton Affair — Incident where Mexican forces killed 11 U.S. soldiers, initiating war.
- Bear Flag Republic — Short-lived independent California state declared by American settlers.
- Treaty of Guadalupe Hidalgo — Agreement ending the war, transferring vast territory from Mexico to the U.S.
- Mexican Cession — Land Mexico ceded to the U.S., including CA, NV, UT, AZ, NM, CO, WY.
- Manifest Destiny — Belief in the U.S. right to expand across the continent.
Action Items / Next Steps
- Review the political impact of the Mexican Cession on the slavery debate.
- Read about key figures: Polk, Taylor, Santa Anna, Fremont, and Scott.
- Examine maps of the Mexican Cession and campaign routes for context.