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Understanding the Mexican-American War

Apr 8, 2025

Heimler's History: Mexican-American War

Overview

  • Focus on Unit 5 of the AP U.S. History curriculum.
  • Main question: What were the causes and effects of the Mexican-American War?

Causes of the Mexican-American War

  • Texas Independence

    • Texas declared independence from Mexico in 1836.
    • Tensions between Mexico and Texas cooled when Texas remained independent.
  • Annexation of Texas

    • Texans wanted to be annexed by the U.S., which Mexico opposed.
    • Presidents Jackson, Van Buren, Harrison, and Tyler avoided annexation.
    • James K. Polk, elected in 1845, promised the annexation of Texas.
    • John Tyler initiated the annexation process before leaving office.
  • Disputed Territory

    • Polk sent diplomat John Slidell to Mexico City:
      • Proposed purchasing New Mexico and California territories.
      • Attempted to settle the border dispute: U.S. claimed the Rio Grande; Mexico claimed the Nueces River.
    • Slidell’s missions failed; Mexico refused both propositions.
  • Military Actions

    • Polk sent General Zachary Taylor to advance to the Rio Grande.
    • Clash with Mexican troops resulted in 11 American deaths.
    • Polk used the incident to justify a war with Mexico.
    • Congress declared war on May 13, 1846.

Effects of the Mexican-American War

  • Territorial Gains

    • Treaty of Guadalupe Hidalgo (1848):
      • Established Rio Grande as the border.
      • Mexican Cession: Mexico ceded California and New Mexico for $15 million.
      • Mexico lost over half its territory.
  • Wilmot Proviso (1846)

    • Proposed banning slavery in any territory gained from Mexico.
    • Highlighted tensions over slavery.
    • Although voted down, it signaled rising conflict leading to the Civil War.
  • Impact on Non-American Residents

    • Mexicans in ceded territories granted U.S. citizenship.
    • Indigenous peoples were not granted citizenship until the 1930s.
    • Faced civil rights challenges, including voter discrimination and educational segregation.

Conclusion

  • Unit 5 Topic 3 of the AP U.S. History curriculum covers crucial aspects of the Mexican-American War.
  • Understanding these details is essential for performing well in exams.
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