The Mexican-American War was fought between Mexico and the United States from 1846 to 1848. It was a defining moment in the relationship between the two countries and shaped the borders of the southwestern United States as we know them today.
The main leaders of the Mexican army during the Mexican-American War were:
- General Antonio López de Santa Anna – President of Mexico and commander of the Mexican Army
- General Pedro de Ampudia – Commander of the Army of the North
- General José Mariá Flores – Commander of the Army of the Center
- General Francisco Mejía – Commander of the Army of the North after Ampudia
General Santa Anna was the key strategic leader of the Mexican forces during the war, though his battlefield leadership was often questionable. Other generals like Ampudia, Flores, and Mejía led the major regional Mexican armies that fought against the U.S. invasion.
Causes of the Mexican-American War
There were several key factors that led to the outbreak of the Mexican-American War in 1846:
- Texas – The United States annexed Texas in 1845, a territory that Mexico still considered part of its country after Texas independence in 1836. This was a major point of contention between the U.S. and Mexico.
- Border Disputes – There was disagreement on where the border between Texas and Mexico actually was, with both countries claiming territory between the Nueces River and the Rio Grande.
- Manifest Destiny – Many Americans believed it was their country’s manifest destiny to expand across the continent to the Pacific Ocean, including into Mexican territory.
- Mexican Politics – Political instability and nationalism in Mexico opposed American expansionism into traditionally Mexican lands.
In 1845, President James K. Polk sent troops under General Zachary Taylor to the disputed Texas border area. In April 1846, Mexican and American troops skirmished, beginning the war.
Overview of the Mexican Military
At the outset of the war, the Mexican military was unprepared and at a disadvantage compared to the United States:
- Smaller population and industrial capacity than the U.S. – limiting recruits and supplies
- Political instability – multiple coups in the years prior
- Limited funding and supplies for the army
- Poor roads and infrastructure, making movement difficult
- Regionalism – distrust between different Mexican regions
Despite these challenges, some Mexican military leaders tried to modernize prior to the war by adopting more professional training and equipment. The majority of troops though remained poorly trained, equipped, and led during the conflict.
Mexican Army Organization
The Mexican army that fought the war was organized into regional commands:
- Army of the North – Defended the northern Mexican states and faced off against American forces invading from Texas and New Mexico.
- Army of the Center – Defended the central Mexican states and the approaches to Mexico City itself. It also faced some American naval attacks along the coast.
- Army of the East – A smaller force defending the Gulf coast region near Tampico and Veracruz.
- Various garrisons – Scattered throughout Mexico to provide local defense.
Though numbering perhaps 50,000 men, logistical difficulties, poor training, and internal divisions prevented the coordination needed for an effective defense.
Weapons and Equipment
The weapons and equipment of the Mexican army generally lagged behind that of the Americans:
- Smoothbore Muskets – The main infantry weapon, accurate only to 100 yards or less.
- Artillery – Lacked the range, accuracy, and mobility of American guns.
- Lances – Used by some cavalry units in traditional fashion.
Supplies like gunpowder and spare parts were also often in short supply. The limited Mexican industry could not keep up with wartime needs. Weapons procured from Europe were frequently old or obsolete models.
Key Mexican Commanders
The most prominent leaders of the Mexican army during the war included:
General Antonio López de Santa Anna
As president of Mexico and commander of the army, Santa Anna was the leading strategic decision-maker for the Mexican war effort. His most important decisions included:
- Trying to crush the American force at the outset of the war along the Rio Grande.
- Repealing a law that would have allowed more indigenous recruits into the army.
- Personally marching north with the Army of the North to fight Taylor’s invasion.
- Withdrawing south after his defeat at Buena Vista to deal with American landings at Veracruz.
Santa Anna had a reputation as an opportunist, switching sides during Mexico’s years of political turmoil. His battlefield leadership during the war proved poor. However, his name recognition and political stature allowed him to remain Mexico’s commander in chief throughout the conflict.
General Pedro de Ampudia
General Pedro de Ampudia led the Army of the North at the outset of the war in northern Mexico. As commander along the Rio Grande, he:
- Established defensive fortifications along the river.
- Initiated the Siege of Fort Texas, the first engagement of the war.
- Was defeated by Taylor at the Battle of Monterrey.
Ampudia was an experienced officer who had earlier served against Texas rebels and indigenous groups. Though forced to withdraw after Monterrey, he gave Taylor’s army its first real fight of the war.
General Francisco Mejía
Mejía replaced Ampudia as head of the Army of the North prior to the crucial Battle of Buena Vista in February 1847. He:
- Encouraged Santa Anna to engage Taylor along a narrow mountain pass.
- Commanded the senior infantry division in the battle itself.
- Helped cover Santa Anna’s retreat after the Mexican defeat.
Though Mejía could not prevent yet another loss to Taylor in the north, he did show tactical initiative during the battle that was often lacking among Mexican commanders.
Major Campaigns and Battles
The Mexican army fought against American offensives on multiple fronts during the war, though they were unable to halt U.S. advances:
Northern Mexico Theater
- Battle of Palo Alto (May 8, 1846) – Opening battle of the war, American victory that drove Mexicans across the Rio Grande.
- Battle of Resaca de la Palma (May 9, 1846) – Second American victory allowing Taylor to cross into contested territory.
- Battle of Monterrey (September 21-24, 1846) – Hard fought American capture of a key city in northern Mexico.
- Battle of Buena Vista (February 22-23, 1847) – Santa Anna failed to defeat Taylor’s army in a bloody mountain pass clash.
Though fighting gamely, the Army of the North was steadily driven southward by General Taylor’s force. Mexico failed to expel American troops from northern Mexico.
Central Mexico Theater
- Siege of Fort Texas (April 30 – May 9, 1846) – First siege of the war ended by Taylor’s relief force.
- Battle of Cerro Gordo (April 17-18, 1847) – General Winfield Scott defeated Santa Anna in a surprise flank attack while driving on Mexico City.
- Battle of Contreras (August 19-20, 1847) – Part of a string of American victories outside Mexico City leading up its capture.
The Army of the Center tried to defend the approaches to Mexico City itself but was outmaneuvered by Scott. Mexico’s capital fell in September 1847.
Northeastern Mexico Theater
- Veracruz Campaign (March 9–29, 1847) – Successful American amphibious landing and siege of the strategic port city.
- San Juan de Ulúa Siege (March 25 – September 8, 1847) – American blockade forced the surrender of the offshore Mexican fortress guarding Veracruz.
Though smaller in scale, fighting in northeastern Mexico conquered the country’s main Atlantic port for American resupply and reinforcement.
Reasons for Mexico’s Defeat
There were several interrelated reasons why Mexico ultimately lost the war against the United States:
- Weaker military leadership – Santa Anna and other leaders proved inept or ineffective.
- Divided military effort – Lack of coordination between Mexico’s regional armies.
- Technological imbalance – Mexico lacked the industry to produce modern weapons or supplies.
- Unstable politics – Frequent coups and regionalism undermined the national war effort.
- Manpower shortage – Mexico had one-seventh the U.S. population to draw soldiers from.
- Faulty strategy – Attempts to defend everywhere while attacking nowhere.
Together these factors hindered an effective national defense, despite the determination of individual Mexican units and leaders at certain points in the war.
Consequences and Impact
The Mexican defeat in the Mexican-American War had enormous consequences for both countries:
- Mexico lost about 1/3 of its territory to the United States, including nearly all the present-day American Southwest.
- The annexation of Texas, California, and New Mexico strengthened the Union as it moved towards the Civil War.
- The war discredited Santa Anna and fueled further political turmoil in Mexico.
- The perceived injustice of the war strengthened Mexican nationalism and anti-American sentiment.
The human and material costs of the war were high as well. Mexico lost at least 25,000 men killed in action. The post-war payment from Mexico to the U.S. of $15 million further strained the Mexican economy for decades to come.
The Mexican-American War represented a key turning point for North America, establishing the continental boundaries that largely remain to this day. Poorly led and coordinated, the Mexican military was unable to blunt the drive of American forces steadily capturing control of the country.
While Mexicans like Santa Anna, Ampudia, and Mejía fought valiantly at times, they were outmatched strategically and militarily by American generals like Taylor and Scott. Mexico was overwhelmed by its more populous northern neighbor, losing nearly half its territory. The lingering legacy of the war would cast a long shadow over Mexican-American relations for generations to come.