Battle of Churubusco in the Mexican-American War.

Mexican American War

By the early 1840s, the United States' slow and gradual push Westward had already begun. With a steadily growing population now reaching around 18 million, new states and territories were being settled and formed in rapid succession. The evermore popular idea of "Manifest Destiny" was being effectively championed by large segments of the American political class and endlessly pushed onto the public with stunning effectiveness.

This idea proposed that the American people had a divine destiny and, therefore a right from God himself to conquer or colonize the remainder of the North American continent all the way to the Pacific coast. This land that the United States claimed, was already inhabited by numerous Indigenous Peoples. However, the Native Americans were not alone in obstructing this plan. Much of the land that the United States was aiming to settle was already under the control of the newly formed Mexican Empire.

Lead Up to the War

Black and white of the Inauguration of President Polk
 Inauguration of President Polk.

Upon gaining its independence in 1821, Mexico inherited the large swathe of territory that was conquered by the Spanish centuries prior. Nearly one-third of this land consisted of what today makes up the states of California, Utah, Nevada, Arizona, and New Mexico. It was this land in particular that the United States was keen to annex.

Tensions between the two nations began to build in 1836 when Texas, a state within Mexico, declared its independence. Texas was home to a large segment of white, English-speaking, Protestant settlers who originated from the United States and Europe. Sharing little in common with their Mexican compatriots, the Texans won themselves the right to self-determination after a short war against the Mexican military.

Although independent, it was clear to the American, Mexican, and Texan governments that becoming a part of the United States was inevitable as soon as independence was achieved. In 1845, Texas was officially annexed by the United States, much to the chagrin of Mexico.

The same year, the imperialist candidate James Polk was elected to office with the clear goal of expanding the borders of the United States westward. Polk and his government offered to buy the vast territories of Northern Mexico for the price of $30 million (1.2 billion in today's money) but this offer was refused by Mexican authorities. Both Mexican and American soldiers were dispatched and sent to project power in the disputed territories. At this point, it was clear that direct and open war was on the horizon. All it would take was one single match to engulf the entire region in a bloody and savage conflict.

The War Begins

Battle of Veracruz during the Mexican-American War
Battle of Veracruz during the Mexican-American War.

Mexico struck the first blow. In April 1846, a small group of Mexican soldiers ambushed an American patrol along the Rio Grande River. After this initial skirmish, a larger Mexican force numbering around 3,400 poured across the border and surrounded Fort Texas, laying siege to the settlement. General Zachary Taylor, the man in charge of American forces in the Southern United States, frantically assembled what little men he could in response.

Despite catching the American army by surprise, the Mexicans were unable to gain the advantage. The Mexican military was chronically undersupplied and lacked the logistical infrastructure to launch a large and meaningful offensive deep into American territory. Lacking arms, organization, and proper leadership, what little momentum they had in the early days of the war quickly fizzled out. By May 8th, fast-approaching American relief had reached the fort, forcing the Mexican army to abandon the siege and start their retreat toward the border.

Taylor was able to muster nearly 2,400 men. This was a sizable army for the time but was still outnumbered by nearly 1,000 soldiers. Suffering a severe numerical disadvantage, Taylor and the Americans were still able to score decisive victories against the Mexicans at the Battle of Palo Alto and the Battle of Resaca de la Palma.

Deep Into Mexico

Battle of Molino del Rey during the Mexican-American War, painting by Carl Nebel.
Battle of Molino del Rey during the Mexican-American War.

With much of the Mexican resistance in the North destroyed, American troops were free to push into the disputed territories. The Mexican frontier was sparsely populated and only had a population of around 75,000. The residents of this area could do little to stop the American advance and failed to mount significant resistance against the occupation.

In an act of desperation, the Mexican government recalled the famed Mexican strongman Antonio López de Santa Anna. The heavy-handed general was living in exile in Cuba but was quickly ferried over on August 6th, 1846, and was given direct control of the army.

Santa Anna, the last hope of the Mexican cause, met American forces at the Battle of Buena Vista in 1847 but was soundly defeated and took heavy casualties. To make matters worse, the Americans had landed another force at Veracruz and were marching on Mexico City.

The Mexicans still offered up stiff resistance against American forces but were unable to claim any more victories aside from a handful of skirmishes. By 1848, Mexico City was occupied, and the war was essentially over. In February of that year, the Treaty of Guadalupe Hidalgo was signed, bringing an official end to the war.

Large sections of the Mexican government were concerned that Santa Anna would make himself dictator once again if he was given power over the military. While it is not clear what Santa Anna intended to do if he had won the war, he was never given the opportunity and instead retired to Jamaica in 1847, defeated.

A Difference In Supply and Training

Storming of Chapultepec – Quitman's attack (September 13, 1847) in the Mexican-American War.
Storming of Chapultepec, Quitman's attack in the Mexican-American War.

The performance of the Mexican military during the war was less than stellar despite having a numerical advantage throughout the conflict. Even though the Mexicans were able to field more soldiers, it was the quality of training and cutting-edge technology that ultimately won the Americans the war.

The average Mexican soldier was often poorly trained and lacked access to proper equipment. Mexican artillery and gunpowder were considerably worse than their American counterpart and often needed to be shoddily repaired in the field. It was not uncommon for entire batteries of Mexican artillery to malfunction during battles or to miss their target, rendering them nearly useless.

Lost rifles and other equipment could not be easily replaced either, making each defeat all that more costly. Even though the Mexican fighting spirit was on full display on multiple occasions, it ultimately fell short of an American force that benefited from superior logistics, leadership, and military technology. In almost all of the American major victories, the American artillery won them the day with reliable and accurate fire.

Aftermath of the War

General Scott's entrance into Mexico in the Mexican-American War.
General Scott's entrance into Mexico City in the Mexican-American War.

With the treaty in full effect, the Mexican government was forced to accept the Rio Grande as the new border between Mexico and the United States and cede all of its Northern territory. The American government did pay them for the land that was given to them, but it was at the discounted price of 15 million dollars rather than the original 30 million that was initially offered.

The United States suddenly found itself in charge of just over 525,000 square miles of new territory and tens of thousands of new citizens. Many of the Mexicans who lived in the lost territories migrated back to Mexico, but a substantial number also stayed on the land that they had settled.

Only a few years later, in 1848, gold was discovered in California, which triggered a mass wave of migration into the area. Even though the conflict was short-lived and relatively one-sided, it forever changed the destiny of both nations for better or worse.


The Mexican-American War is an often overlooked part of American history despite it having such a profound impact on the nation. The acquisition of new land brought immense wealth and power to the United States, but it also came with plenty of struggles.

The issue of slavery would dominate political discourse for the next 12 years, and the decision to make California a free or slave state only made the animosity in the nation worse. With one side wanting to stem the growth of slavery and the other wanting to expand it, new territory only raised the stakes between the two parties and would end up being one of the leading causes of the American Civil War, which broke out in 1861. Ironically, many of the soldiers and commanders of this war went on to fight another just a few years later.


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