Military Veterans Project

The Mexican American War

April 25, 1846 February 12, 1848


The US was unprepared for war in 1846. Many senior leaders of the US forces had entered service before the War of 1812 and were too old for active duty. Additionally, the number of US Army soldiers was less than 6,000. At the start of the war there were, however, in the graduating classes of West Point many officers who were able to supplement the low number of active officers. Many of these officers would later command the armies during the Civil War.

While the US did have state militia to call upon they by law could only serve for 90 days. To allow for longer service Congress created "Volunteers Soldiers" and 50,000 volunteer troops were raised to serve for 12 months. In November 1846 Congress called upon a new set of volunteers who signed up to fight the duration of the war and created ten additional regiments of regular US soldiers. Close to 27,000 regulars and over 73,000 volunteers were utilized to fight the conflict.

The start of the War goes back to 1836 when Texas gained its independence from Mexico. The US did not initially make Texas a state as it would have added to the number of existing slave states. At the same time the Mexican government indicated that any annexation of Texas would lead to war. Border raids were becoming more common.

In 1844 President Polk campaigned to re-annex Texas and also the Oregon Territory. Polk also wanted to include California, New Mexico and the rest of the Southwest. Polk's offer to purchase the lands was rejected by Mexico. Polk provoked the Mexican government by positioning US troops between the Rio Grande and Nueces River. An area that both countries had recognized as being part of Mexico.

April 25, 1846 saw Mexican cavalry attack a unit of US soldiers under the command of General Zachary Taylor. Mexican troops then attacked an American Fort on the Rio Grande. However, Taylor along with better equipped reinforcements were able to defeat the Mexican Army at the battle of Palo Alto and Resaca de la Palma.

On May 13, 1846 Congress officially declared war. With only 75,000 Mexican citizens in the area of the Rio Grande, the US Army was able to take the lands with little resistance. General Taylor was able to take Monterrey in September 1846. At this point Mexico recalled General Antonio Lopez de Santa Anna from exile in Cuba. Santa Anna convinced President Polk that he could end the war with favorable terms for the US. However, upon Santa Anna's return he took control of the Mexican troops to fight against the US. The Battle of Buena Vista in February 18, 1845 resulted in Santa Anna having to withdraw because of heavy casualties. This, however, did not stop Santa Anna from assuming the presidency of Mexico in May 1847.

During this time General Winfield Scott took Veracruz and began his march toward Mexico City laying seige to the city in September 1847. While guerrilla attacks were still happening along the US supply line the war was basically over. Santa Anna resigned and when the new government of Mexico was in place the Treaty of Guadalupe Hidalgo was signed. The Rio Grande instead of the Nueces River was now the new US – Mexican border. Also the treaty included recognition of the US annexation of Texas, and for a payment of $15 million plus damage claims the US also gained California, Arizona, New Mexico and parts of Nevada, Colorado and Utah.

US Military Officers in the Mexican American War who also served during The Civil War

Winfield Scott, General Braxton Bragg, Lt Colonel
Robert E Lee, Lieutenant George Meade, Lieutenant
James Longstreet, General Ambrose Burnside, Lieutenant
Ulysses S Grant, Lieutenant George McClellan, Lieutenant
Thomas “Stonewall” Jackson, Lieutenant William Tecumseh Sherman, Lieutenant
Pierre Gustave Toutant Beauregard, Lieutenant

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