The MEXICAN-AMERICAN War [APUSH Review Unit 5 Topic 3] Period 5: 1844-1877

Causes of the Mexican-American War

• Texas Independence

  • Texas declared independence from Mexico in 1836 and engaged in several battles for freedom.

  • Mexico was unwilling to accept Texas's independence and did not concede defeat fully.

• Desire for Annexation

  • Texans sought annexation by the United States, which angered Mexico.

  • Presidents Jackson, Van Buren, Harrison, and Tyler avoided annexation due to these tensions.

• Election of James K. Polk

  • Polk, elected in 1844, made annexation of Texas a key campaign promise.

  • Despite Tyler’s predecessor efforts, it was Polk’s election momentum that made annexation politically viable.

• Diplomatic Tensions

  • Upon taking office, Polk faced discontent in Mexico over Texas's annexation.

  • Diplomat John Slidell sent to negotiate:

    • Purchase of New Mexico and California territories.

    • Disputed border claims: Mexico claimed the Nueces River, while the U.S. asserted the Rio Grande.

• Military Conflict

  • Polk sent General Zachary Taylor's troops to the Rio Grande.

  • Clashes resulted in 11 American deaths, prompting outrage from Polk.

  • On May 13, 1846, Congress declared war on Mexico, igniting the Mexican-American War.

Effects of the Mexican-American War

• Territorial Gains for the U.S.

  • Treaty of Guadalupe Hidalgo (1848) formalized territorial losses for Mexico.

    • Rio Grande established as Texas's southern border.

    • Mexican Cession: California and New Mexico ceded to the U.S. for $15 million.

• Wilmot Proviso

  • Proposed by Congressman David Wilmot during the war to prohibit slavery in new lands acquired from Mexico.

  • Highlights rising tensions about slavery, though it was ultimately defeated.

  • Seen as a precursor to conflict leading to the Civil War.

• Impact on Non-American Inhabitants

  • Majority of Mexicans and Native Americans remained after territorial transition.

  • Treaty promised U.S. citizenship to Mexicans but excluded Native Americans, delaying citizenship until the 1930s.

  • Both groups faced extensive civil rights issues, including voting discrimination and segregation in education.