Heimler APUSH TP 5.3

The Mexican-American War: Causes and Effects

Introduction

• Focus on understanding the causes and effects of the Mexican-American War.

Causes of the Mexican-American War

• Texas Independence

  • Texas declared independence from Mexico in 1836.

  • Fought several battles to achieve independence.

• Annexation of Texas

  • Post-independence, Texans desired annexation by the United States.

  • The Mexican government viewed this desire as a hostile act.

• Presidential Opposition

  • Presidents Jackson, Van Buren, Harrison, and Tyler opposed annexation initially.

  • The election of James K. Polk in 1844 changed the situation; Polk favored annexation.

• Annexation Timeline

  • While Polk is associated with the annexation, it was John Tyler who started the process.

• Diplomatic Tensions

  • Polk sent diplomat John Slidell to Mexico City.

    • Requested the sale of New Mexico and California territories.

    • Sought to clarify the southern border dispute.

• Border Dispute

  • Mexico claimed the Nueces River as the border; the U.S. claimed the Rio Grande.

  • Reluctance from the Mexican government to negotiate.

• Military Escalation

  • In 1846, Polk ordered General Zachary Taylor to station troops at the Rio Grande.

  • Skirmishes led to American casualties and escalated demands for war.

• Declaration of War

  • Polk gained congressional approval for war on May 13, 1846, framing it as a defense of U.S. territory.

Effects of the Mexican-American War

• Territorial Gains

  • Treaty of Guadalupe Hidalgo (1848) resulted in significant land acquisition for the U.S.

    • Established Rio Grande as the southern border of Texas.

    • Mexico ceded California and New Mexico for $15 million.

  • Speculative total loss for Mexico was over half its territory.

• Wilmot Proviso

  • David Wilmot proposed an amendment to prevent the expansion of slavery into newly acquired territories.

  • The proposal was ultimately voted down but signified tensions surrounding slavery.

  • It highlighted the economic motivations of politicians preferring free soil over moral considerations regarding slavery.

  • Many historians see the Wilmot Proviso as a precursor to the Civil War.

• Impact on Non-American Citizens

  • Many Mexicans and Native Americans remained in U.S.-acquired territories post-war.

  • Treaty agreed to grant U.S. citizenship to Mexicans in the territory.

  • Native Americans did not receive similar citizenship offers until the 1930s.

  • Both groups faced discrimination including voter disenfranchisement and educational segregation.