10 Facts About the Mexican-American War

The USA Invades Its Neighbor to the South

The Mexican-American War (1846-1848) was a defining moment in the relationship between Mexico and the USA. Tensions had been high between the two since 1836 when Texas broke off from Mexico and began petitioning the USA for statehood. The war was short but bloody and major fighting ended when the Americans captured Mexico City in September of 1847. Here are ten facts you may or may not know about this hard-fought conflict.

The American Army Never Lost a Major Battle

The Battle of Resaca de la Palma

U.S. Army/Wikimedia Commons/Public domain

The Mexican-American War was waged for two years on three fronts, and clashes between the American army and the Mexicans were frequent. There were about ten major battles: fights which involved thousands of men on each side. The Americans won all of them through a combination of superior leadership and better training and weapons.

To the Victor the Spoils: The US Southwest

Battle of Palo Alto

MPI/Getty Images

In 1835, all of Texas, California, Nevada, and Utah and parts of Colorado, Arizona, Wyoming, and New Mexico were part of Mexico. Texas broke off in 1836, but the rest was ceded to the USA by the Treaty of Guadalupe Hidalgo, which ended the war. Mexico lost roughly half of its national territory and the USA gained its vast western holdings. The Mexicans and Indigenous people who lived in those lands were included: they were to be given US citizenship if they wished, or were allowed to go to Mexico.

The Flying Artillery Arrived

Battle Of Pueblo De Taos

Kean Collection/Getty Images

Cannons and mortars had been part of warfare for centuries. Traditionally, however, these artillery pieces were hard to move: once they were placed before a battle, they tended to stay put. The US changed all that in the Mexican-American war by deploying the new "flying artillery:" cannons and artillerymen that could be quickly redeployed around a battlefield. This new artillery wreaked havoc with the Mexicans and was particularly decisive during the Battle of Palo Alto.

Conditions Were Abominable

General Winfield Scott Entering Mexico
General Winfield Scott entering Mixico City on horseback (1847) with the American Army.

Bettmann Archive/Getty Images

One thing united American and Mexican soldiers during the war: misery. Conditions were terrible. Both sides suffered greatly from disease, which killed seven times more soldiers than combat during the war. ​General Winfield Scott knew this and deliberately timed his invasion of Veracruz to avoid the yellow fever season. Soldiers suffered from a variety of diseases, including yellow fever, malaria, dysentery, measles, diarrhea, cholera, and smallpox. These illnesses were treated with remedies such as leeches, brandy, mustard, opium, and lead. As for those wounded in combat, primitive medical techniques often turned minor wounds into life-threatening ones.

The Battle of Chapultepec Is Remembered by Both Sides

The Battle of Chapultepec
The Battle of Chapultepec.

E.B. & E.C. Kellogg (Firm)/Wikimedia Commons/Public domain

It wasn't the most important battle of the Mexican-American War, but the Battle of Chapultepec is probably the most famous one. On September 13, 1847, American forces needed to capture the fortress at Chapultepec–which also housed the Mexican Military Academy–before advancing on Mexico City. They stormed the castle and before long had taken the city. The battle is remembered today for two reasons. During the battle, six courageous Mexican cadets - who had refused to leave their academy–died fighting the invaders: they are the Niños Heroes, or "hero children," considered among the greatest and bravest heroes of Mexico and honored with monuments, parks, streets named after them and much more. Also, Chapultepec was one of the first major engagements in which the United States Marine Corps took part: marines today honor the battle with a blood-red stripe on the trousers of their dress uniforms.

It Was the Birthplace of Civil War Generals

Grant and His Generals by Ole Peter Hansen Balling

Corbis/Getty Images

Reading the list of junior officers who served in the US Army during the Mexican-American War is like seeing a who's who of the Civil War, which broke out thirteen years later. Robert E. Lee, Ulysses S. Grant, William Tecumseh Sherman, Stonewall Jackson, James Longstreet, P.G.T. Beauregard, George Meade, George McClellan, and George Pickett were some–but not all–men who went on to become Generals in the Civil War after serving in Mexico.

Mexico's Officers Were Terrible

Portrait of Santa Anna
Antonio Lopez de Santa Anna on horseback with two aides.

Corbis/Getty Images

Mexico's Generals were dreadful. It's saying something that Antonio Lopez de Santa Anna was the best of the lot: his military ineptitude is legendary. He had the Americans beaten at the Battle of Buena Vista, but then let them regroup and win after all. He ignored his junior officers at the Battle of Cerro Gordo, who said the Americans would attack from his left flank: they did and he lost. Mexico's other generals were even worse: Pedro de Ampudia hid in the cathedral while the Americans stormed Monterrey and Gabriel Valencia got drunk with his officers the night before a major battle. Often they put politics before victory: Santa Anna refused to come to the aid of Valencia, a political rival, at the Battle of Contreras. Although the Mexican soldiers fought bravely, their officers were so bad that they nearly guaranteed defeat at every battle.

Their Politicians Weren't Much Better

Battle of Churubusco

John Cameron and Nathaniel Currier/Wikimedia Commons/Public domain

Mexican politics was completely chaotic during this period. It seemed as if no one was in charge of the nation. Six different men were President of Mexico (and the presidency changed hands nine times among them) during the war with the USA: none of them lasted longer than nine months, and some of their terms in office were measured in days. Each of these men had a political agenda, which often was directly at odds with that of their predecessors and successors. With such poor leadership on a national level, it was impossible to coordinate a war effort among various state militias and independent armies run by inept generals.

Some American Soldiers Joined the Other Side

Mexican-American war

Mansfield, Edward Deering, 1801-1880/Wikimedia Commons/Public domain

The Mexican-American War saw a phenomenon that is nearly unique in the history of war–soldiers from the winning side deserting and joining the enemy! Thousands of Irish immigrants joined the US army in the 1840s, looking for a new life and a way to settle in the USA. These men were sent to fight in Mexico, where many deserted because of harsh conditions, lack of Catholic services and blatant anti-Irish discrimination in the ranks. Meanwhile, Irish deserter John Riley had founded the St. Patrick's Battalion, a Mexican artillery unit comprised mostly (but not completely) of Irish Catholic deserters from the US army. The St. Patrick's Battalion fought with great distinction for the Mexicans, who today revere them as heroes. The St. Patrick's were mostly killed or captured at the Battle of Churubusco: most of those captured were later hung for desertion.

The Top US Diplomat Went Rogue in Order to End the War

Nicholas Trist

Louis Braunhold/Wikimedia Commons/Public domain

Anticipating victory, US President James Polk sent diplomat Nicholas Trist to join General Winfield Scott's army as it marched to Mexico City. His orders were to secure the Mexican northwest as part of a peace agreement once the war was over. As Scott closed in on Mexico City, however, Polk grew angry at Trist's lack of progress and recalled him to Washington. These orders reached Trist during a delicate point in negotiations, and Trist decided it was best for the USA if he stayed, as it would take several weeks for a replacement to arrive. Trist negotiated the Treaty of Guadalupe Hidalgo, which gave Polk everything he had asked for. Although Polk was furious, he grudgingly accepted the treaty.

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Minster, Christopher. "10 Facts About the Mexican-American War." ThoughtCo, Oct. 2, 2020, thoughtco.com/facts-about-the-mexican-american-war-2136199. Minster, Christopher. (2020, October 2). 10 Facts About the Mexican-American War. Retrieved from https://www.thoughtco.com/facts-about-the-mexican-american-war-2136199 Minster, Christopher. "10 Facts About the Mexican-American War." ThoughtCo. https://www.thoughtco.com/facts-about-the-mexican-american-war-2136199 (accessed April 2, 2023).