The Mexican-American War

The Mexican-American War lasted from early 1846 to late 1847. Final surrender occurred in February 1848, and it was the first major war Mexico fought as an independent country and the first major war America fought to expand its territory. Mexico suffered defeat and lost almost a third of its territory to the United States.

Causes of the Mexican-American War

American President James K. Polk, who assumed office in 1844, had adopted an aggressive policy to ensure the completion of "Manifest Destiny". This was the belief that the United States had a God-given right to eventually control the entire continent. Americans migrating West thought they could manage the land better than Native American nations or the Mexican government.

Mexico had gained independence from Spain in 1821 and political instability was rampant. The government had begun allowing Americans to settle in Mexico's Northern territories to populate them, under the conditions that the newcomers swore an oath of allegiance to Mexico and converted to Catholicism. However, settlers in Texas eventually grew unhappy with the Mexican government's policies and revolted.

Mexico in 1824

© Giggette - Mexico, 1824

Texas eventually declared independence from Mexico in 1836 and spent a brief time as a sovereign state. The United States was not initially interested in annexing Texas, as the majority of US politicians were not interested in adding another slave state.

The United States eventually annexed Texas in 1845, which escalated growing tensions between the United States and Mexico. Polk offered to buy some of the land that now makes up South-Western USA, mainly California, but the Mexican government refused. Border skirmishes, coupled with Polk's desire for a war to claim Mexican territory, caused all-out war to finally began.

The Congress officially declared war after Mexican troops fired on American soldiers, resulting in the deaths of a dozen US soldiers and the occupation of Fort Texas north of the Rio Grande.

Map of the Mexican-American War

© Kaidor - Map of the Mexican-American War

Mexican Troops and Leaders

Antonio Lopez de Santa Anna, Oil Painting

Antonio Lopez de Santa Anna

The most famous Mexican involved in the Mexican-American War was Antonio Lopez de Santa Anna. He was a dynamic figure of Mexican politics for many years, having gone through multiple presidencies, leading the army as a general, and even exile.

It was his capture that ended the revolution of Texas and brought the territory independence. He first became a hero after preventing Spain from trying to reclaim Mexico in 1829.

Other Mexican generals included:

  • General Pedro de Ampudia, who fought the American army at Monterey and was forced to relinquish the city.
  • General Juan Morales, who out of fear resigned his commission but refused to surrender Veracruz to General Winfield Scott.
  • Brigadier General Jose Juan Landero, who called a truce and surrendered Veracruz.

US Troops and Leaders

James K. Polk

James K. Polk

James K. Polk, president from 1845-1849, was the leader of the United States at the time of the conflict.

The other well-known American figure from the war was future US president Zachary Taylor. Taylor would be elected into office after Polk's final term, due to the popularity he generated in the Mexican-American War.

Zachary Taylor was sent to the border with Mexico in the 1840s and remained the general in charge of the American troops throughout the war. A man who preferred a simple appearance, many soldiers commented he looked more like a farmer than a general in his straw hat and linen duster. The nickname he earned was "Old Rough and Ready".


Depiction of Zachary Taylor at Palo Alto

© Mpinedag - Zachary Taylor at Palo Alto


Other American generals included:

  • General David Twiggs, who successfully helped capture Mexico City and was named the military governor of Veracruz. After the war, he commanded the Department of Texas.
  • General Winfield Scott, a career general who fought and commanded in most of America's early wars, from the War of 1812 to the Civil War. Responsible for leading the army that captured Mexico City, he briefly served as military governor of Mexico City after the war.
  • General William Worth, who commanded a brigade under Zachary Taylor and participated in many battles of the war, including the captures of Monterey, Veracruz, and Mexico City.
Disembarkment in Tabasco

© Alfonsobouchot - Disembarkment in Tabasco

Campaigns and Battles

  • The first battle of the war was the Battle of Palo Alto on May 8, 1846. The result was a decisive victory for the United States.
  • The Battle of Monterey was fought between September 20-24, 1846. American troops took the city of Monterey and forced General Pedro de Ampudia to surrender.
  • The Battle of Buena Vista, fought between February 22-23, 1847. Mexican troops came very close to overrunning the US army. The US army was able to stop their offensive and the battle ended with both sides withdrawing.
  • The Battle of Veracruz, fought from March 9-29, 1847. The US army laid siege to the city of Veracruz and the city eventually surrendered.
  • The Battles of Contreras and Churubusco, fought between August 19-20, 1847. Won by the Americans, and opened their path to Mexico City.
  • The Battle for Mexico City, fought between September 13-14, 1847. The US army eventually took the city, but resistance was strong from both the Mexican army positioned there as well as the citizens of Mexico City.

The Mexican army did not have the advanced weaponry the American army did, which helped play a major part in their eventual defeat.

Battle of Churubusco, John Cameron

Battle of Churubusco, Depiction by John Cameron

Results of the Mexican-American War

The war resulted in the loss of modern day Arizona, New Mexico, Utah, Nevada, and most of California for Mexico. The treaty that ended the war was known as the Treaty of Guadalupe Hidalgo, which was signed on February 2, 1848. Even today, many Mexicans resent the actions of the United States in this war.

Map of the Mexican Cession of Territories

Mexican Territories Lost after the Treaty of Guadalupe Hidalgo (White)

Facts About the Mexican-American War

  • The war was largely fought over America's desire to achieve "Manifest Destiny" by taking Mexico's lands in the modern American southwest.
  • The war ended in a victory for the Americans, whose victory gained them modern day Arizona, New Mexico, Utah, Nevada, and most of California in exchange for $15 million. The Rio Grande river became the accepted border between the United States and Mexico.
  • Political divisions within Mexico, as well as less-advanced weaponry and a high rate of desertion, were causes of Mexico's defeat.
  • Abraham Lincoln, future president of the United States and a then-member of the House of Representatives, opposed the war.