Mexican War and Imperialism

APUSH Notes

Texan Independence & the Mexican–American War (1820s–1848)

I. American Settlement in Texas (1820s–1830s)

• Mexico gains independence from Spain (1821) and allows U.S. settlers into Texas to develop the region.

• Stephen F. Austin leads settlement under a Mexican land grant (Father of Texas).

• Most settlers were Southern Americans, bringing:

  • Slavery (illegal in Mexico)

  • Protestantism instead of Catholicism

  • Little effort to assimilate into Mexican culture

• By 1835:

  • ~30,000 Americans

  • ~5,000 enslaved people

• Mexican response:

  • Immigration restricted (1830)

  • Slavery reaffirmed as illegal

  • Military posts and customs duties established

II. Rising Tensions with Mexico

Causes of Conflict

• Cultural and language differences

• Americans ignored Mexican laws

• Texans wanted greater political representation

• Trade tied more to the U.S. than Mexico

• Weak Mexican government presence in Texas

Manuel de Mier y Terán Report (1828)

• Warned Texas would revolt if Mexico didn’t act

• Noted:

  • Americans outnumbered Mexicans 10 to 1

  • Americans were better educated and organized

  • Texans already favored separation from Coahuila

• Predicted Texas could spark a national crisis

III. Santa Anna & the Texas Revolution

• Antonio López de Santa Anna:

  • Elected president (1833)

  • Becomes dictator in 1834

  • Dissolves Congress and centralizes power

• Texans initially wanted statehood within Mexico, not independence

• 1835: Texans organize a provisional government and prepare for war

IV. Key Battles of the Texas Revolution

The Alamo (Feb–Mar 1836)

• ~200 Texans and American volunteers (including Davy Crockett)

• Santa Anna defeats defenders

• Survivors executed

• Becomes a symbolic rallying cry

  • “Remember the Alamo!”

Battle of San Jacinto (April 21, 1836)

• Led by Sam Houston

• Texans surprise Mexican forces

• Santa Anna captured

• Mexico forced to recognize Texas independence (Mexican Congress later refuses)

V. Republic of Texas (1836–1845)

• Independent nation known as the Lone Star Republic

• Constitution:

  • Legalized slavery

  • Banned free African Americans

• Sam Houston elected president

• Texas sought annexation to the United States

• Major controversy:

  • Adding a slave state

  • Risk of war with Mexico

VI. Texas Annexation Debate

U.S. Political Conflict

• John Quincy Adams blocks annexation (filibuster)

• Southern leaders push annexation to protect slavery

• John Tyler & John C. Calhoun:

  • Claim Britain plans to abolish slavery in Texas

• Election of 1844:

  • James K. Polk supports Manifest Destiny

  • Defeats Henry Clay

• 1845: Texas annexed by joint resolution

  • Becomes the 28th state

VII. Causes of the Mexican–American War

• Mexico never accepted Texas independence

• Dispute over boundary:

  • U.S.: Rio Grande

  • Mexico: Nueces River

• Polk sends Zachary Taylor to disputed land

• April 25, 1846: Mexican troops clash with U.S. forces

• Polk claims:

  • “American blood shed on American soil”

• Congress declares war: May 13, 1846

VIII. Mexican–American War (1846–1848)

Major Battles

• Palo Alto & Resaca de la Palma

• Monterrey

• Buena Vista

• Vera Cruz

• Chapultepec

• U.S. captures Mexico City (1847)

Key Leaders

• Zachary Taylor: Northern campaign

• Winfield Scott: Southern campaign, captures Mexico City

IX. Treaty of Guadalupe Hidalgo (1848)

• War officially ends

• Mexico cedes:

  • California

  • New Mexico

  • Southwest territory

• U.S. pays $15 million

• Rio Grande recognized as Texas border

X. Slavery & Sectional Conflict

Wilmot Proviso (1846)

• Proposed banning slavery in territories taken from Mexico

• Passed House, failed Senate

• Deepened sectional tensions

Free Soil Party (1848)

• Opposed expansion of slavery

• Slogan:

  • “Free soil, free speech, free labor, free men”

XI. Opposition to the War

Anti-War Critics

• Henry David Thoreau

  • Refused to pay taxes

  • Wrote Civil Disobedience

  • Inspired Gandhi & MLK Jr.

• Abraham Lincoln

  • Introduced Spot Resolutions

• Henry Clay, John Quincy Adams, William Lloyd Garrison

• War seen as:

  • Imperialistic

  • Pro-slavery

  • Morally unjust

Reality of the War

• More deaths from disease than combat

• Reports of U.S. brutality against civilians

• Irish-Catholic soldiers defected to Mexico (San Patricio Battalion)

XII. Historical Significance

• Fulfilled Manifest Destiny

• Intensified sectional conflict over slavery

• Set stage for:

  • Compromise of 1850

  • Civil War

• Raised questions about:

  • Moral limits of expansion

  • Power of civil disobedience

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