Mexican-American War Overview

Overview

This lecture covers the Mexican-American War (1846–1848), its causes, key strategies, major outcomes, and its significance in U.S. territorial expansion and political history.

Causes and Background

• The war began as President Polk sought to annex Texas and expand U.S. territory.
• Texas was an independent nation before annexation; Polk's opponents called it "Polk's War" due to his motives.
• The conflict fits into broader U.S. westward expansion and manifest destiny ideology.

Strategies and Advantages

• Polk aimed for a short, inexpensive war for quick morale-boosting victory.
• The U.S. army had fewer than 10,000 troops, relying on a one-year volunteer plan and naval superiority.
• Mexico aimed to retake Texas and damage American morale, with 20,000 troops and challenging home terrain.
• Mexico hoped for European help, but the Monroe Doctrine kept Europe out.
• U.S. benefited from better-trained officers (West Point) and strong public support for expansion.

Key Campaigns and Battles

• U.S. forces quickly took California and New Mexico, facing internal leadership conflicts.
• John C. Fremont became a prominent figure in California, later court-martialed but pardoned.
• General Zachary Taylor won key battles but became politically threatening to Polk.
• General Winfield Scott led a successful amphibious assault at Veracruz and captured Mexico City.
• Santa Anna’s return briefly revived Mexican morale but failed to shift the war.

Outcome and Effects

• The Treaty of Guadalupe Hidalgo (1848) ceded vast territories (Texas, California, New Mexico, Arizona, parts of Utah, Colorado, Wyoming, Nevada) to the U.S.
• U.S. nearly doubled in land; later agreements added even more territory.
• The war added to U.S. reputation for military success.
• Many Civil War leaders gained experience in this conflict.
• The war fueled manifest destiny, expansion of slavery debates, and set the stage for the Civil War.
• California's acquisition led directly to the Gold Rush and significant westward migration.

Key Terms & Definitions

• Manifest Destiny — The belief that U.S. expansion across the continent was justified and inevitable.
• West Point — U.S. Military Academy, source of well-trained officers.
• Amphibious Assault — Military attack involving landing forces from the sea onto land.
• Treaty of Guadalupe Hidalgo — 1848 peace treaty ending the war, ceding large Mexican territories to the U.S.
• Monroe Doctrine — U.S. policy opposing European interference in the Americas.

Action Items / Next Steps

• Review territorial acquisitions on a map for better understanding.
• Prepare for discussion on how the war influenced the Civil War and westward expansion debates.