Mexican–American War (1846–1848) Notes

The Treaty of Guadalupe Hidalgo (1848)

Background

• The Treaty of Guadalupe Hidalgo, signed on February 2, 1848, ended the Mexican–American War (1846–1848), a conflict sparked by U.S. expansionist ambitions under Manifest Destiny and the disputed annexation of Texas (1845).
• The war resulted in a decisive U.S. victory and massive territorial losses for Mexico, permanently reshaping North America’s political map.

Terms of the Treaty

• Mexico ceded over 500,000 square miles (about half its territory) to the United States, including present-day California, Nevada, Utah, Arizona, New Mexico, and parts of Colorado and Wyoming.
• The Rio Grande was recognized as the southern border of Texas.
• The United States agreed to pay $15 million in compensation and assume approximately $3 million in Mexican debts owed to American citizens.
• The treaty promised to protect the property, language, and civil rights of Mexicans living in the newly annexed territories.

Causes and Motivations

• Rooted in the ideology of Manifest Destiny, Americans believed they were destined to expand westward across the continent.
• Tensions over the Texas–Mexico border and President James K. Polk’s expansionist policies provoked open war.
• Mexico, politically unstable and militarily weaker, was unable to resist U.S. invasion effectively.

Consequences and Impact

For the United States

• The treaty fulfilled Manifest Destiny, vastly increasing U.S. size and resources.
• It intensified the sectional conflict over whether new territories would allow slavery, contributing to the causes of the American Civil War (1861–1865).
• The victory boosted national pride and the image of U.S. military power.

For Mexico

• Mexico suffered a crushing territorial and psychological loss, fueling long-term resentment toward the United States.
• The loss deepened internal divisions and political instability, weakening Mexico’s government for decades.
• Many Mexicans in annexed regions became second-class citizens, losing land and legal rights despite treaty guarantees.

Legacy

• The Treaty of Guadalupe Hidalgo marked a turning point in U.S.–Mexican relations, symbolizing both American expansionism and Mexican vulnerability.
• It set a precedent for future U.S. territorial acquisitions and imperial ambitions in the Western Hemisphere.
• The treaty remains central to debates about national identity, citizenship, and territorial justice on both sides of the border.

Manifest Destiny and the Mexican–American War (1846–1848)

• Origins of the Idea
  • The term Manifest Destiny was coined by journalist John L. O’Sullivan in 1845, expressing the belief that the United States was divinely ordained to expand across North America. It combined ideas of nationalism, racial superiority, and divine mission, portraying expansion as both inevitable and morally justified.
• Philosophical Foundations
  • Manifest Destiny reflected Enlightenment ideas of progress and liberty, but also a strong sense of Anglo-American exceptionalism. Many Americans believed they were spreading democracy, Christianity, and “civilization” to supposedly less advanced peoples. In reality, it rationalized imperial expansion and displacement of Indigenous and Mexican populations.
• Connection to Expansion and the War:
  • Manifest Destiny provided ideological justification for the annexation of Texas (1845) and the push for new western territories. Expansionists argued that controlling lands from the Atlantic to the Pacific was essential to national destiny. This belief drove President James K. Polk’s aggressive foreign policy, including his pursuit of California and the Oregon Territory.
• Role in the Outbreak of War
  • When Mexico refused to sell its northern provinces, Polk ordered U.S. troops to move into the disputed territory between the Nueces River and the Rio Grande in 1846. A skirmish there provided the pretext to declare war. Manifest Destiny helped frame the conflict as an act of liberation rather than aggression, presenting the war as spreading freedom and opportunity.
• Impact on U.S. Society
  • The ideology inspired migration westward but also deepened sectional tensions. The acquisition of vast new territories reignited debates over slavery’s expansion, contributing to political polarization that later led to the Civil War.
• Impact on Mexico and Indigenous Peoples
  • For Mexico, Manifest Destiny was a disaster, resulting in the loss of about half its territory. For Indigenous peoples, it accelerated forced removals, land seizures, and cultural destruction, as U.S. settlers and armies pushed into new regions. The ideology masked these injustices under the guise of progress and divine purpose.
• Legacy
  • Manifest Destiny became a defining theme of 19th-century American identity, shaping foreign policy long after the war. It reemerged in the Spanish–American War (1898) and later forms of U.S. interventionism in Latin America.