Mexican–American War

The Mexican–American War Summary

The Mexican–American War Despite the discourse surrounding the wall separating the US from Mexico on the US southern border, people often forget that the two countries have engaged in a war in the past. The war between Mexico and the United States of America is among the list of wars that are not relatively well-known despite its irrefutable importance. Even though it was a major war that influenced the developments in North America for years to come (and which effects are still prevalent today),  it can sometimes get overshadowed when people talk about the history of the world. 

The war solved the territorial disputes between the two countries and helped shape  the political geography of the continent; plus, it served as a triumphant victory  for the expansionist US at the time, inspiring it to continue its efforts to pursue its concept of “manifest destiny.”

It also sent Mexico into a further period of instability and economic ruin. Last but not least, it had a socio-cultural impact on both countries, especially with the matter of slavery in the US, which eventually led to the Civil War.

However, we are not here to talk about the aftermath; we are here to talk about the prologue: how did the war start? Both nations taking part in the Mexican-American War were – at some point in their existence – colonies of the Old World.  

Mexico after Independence

The United States managed to gain its independence from the British in 1776, about seventy years before the start of the war.  On the other hand, Mexico became independent from Spain in 1821, about twenty-five years before the start of the war. In the context of the Mexican-American War, it may be more important to understand the Mexican struggle for independence. New Spain – what would later become Mexico – was the largest of Spain’s colonies. On top of that, it was a viceroyalty of the Spanish throne,  making it its own country instead of a colony.  

The population of New Spain was divided heavily among different classes. The system had been developing since the early colonial days, and it assigned privileges to its members based on their racial background.  At the top were the peninsulares, who consisted of Spaniards born in Spain. After then came the criollos, people who were born into peninsular families in the Americas. Below them were the  Indios, people solely of Native American descent, and the mestizos, which included people with one Spanish and one native parent. 

Download this Article in PDF Format

Get a well-documented version of this article for offline reading or archiving.

Download Now (1708 KB)

These last two groups were closely intertwined, with most of them working as artisans and local shopkeepers. Spain was a devoted Roman Catholic nation and had remained so despite the Protestant Reformation, which had transformed the religious landscape of Europe several hundred years before.  

The Spanish conquistadors’ original conquest of the Americas included spreading Catholicism as the prominent faith among the indigenous peoples of the New World. The native population was extremely religious, but by the 1800s, almost all of New Spain had been converted. The natives became firm believers of Catholicism and often incorporated symbolism and imagery from their old religions.

The most prominent example of this merging of the two cultures is probably the legend of the apparition of the Virgin Mary, now referred to as the Lady of Guadalupe,  appearing to an indigenous farmer in 1531. 

Revolution and the growth of industrial society

The events taking place in Europe at the end of the 18th and the beginning of the 19th centuries prompted the spread of revolutionary ideas in New Spain, just as they did in places like Latin America and most of Europe. Of course, the main occurrence during this time was the French Revolution of 1789 and Napoleon Bonaparte’s subsequent rise, which prompted nationalistic movements throughout the Spanish colonies,  including the revolution in Mexico. All of this led to the Mexican War of Independence from 1810  to 1821.

Struggle for Mexican Independence

The Mexicans, just like other peoples of the 19th century, managed to free themselves from the colonial rule of the Europeans, but instead of relief, further instability and internal conflicts continued to plague the country. The social,  racial, political, and religious problems reared their heads time and again. 

In 1833, the Mexican population, especially the conservatives, were enraged by Valentín Gómez Farías’s reforms, which stripped the Catholic  Church of all its lands and reduced its role in education. Antonio López de Santa Anna, a Mexican general who plays a crucial role in this tale, swept in and took the office from Farías. He dissolved Congress, organized a more centralist-conservative government, giving much  of the church’s power back, and introduced a new constitution called the “Seven Laws.”

Causes of the Texas Revolution

All of this led to mass discontent within some of the states of Mexico, most importantly in the state of Texas – then called “Tejas” – which led to the Texas Revolution – one of the main causes of the Mexican-American War. 

Texas had been a disputed region since the early colonial days. It technically belonged to Spain at first, with many Americans claiming it to be a part of the US. This was largely due to the US filibuster mission – privately funded military expeditions that claimed unsettled foreign lands.

US and Spain managed to solve the dispute in 1819 when the US officially relinquished its claims on Texas, establishing the borders that would go on to be a part of the Mexican Republic. To alleviate the issue of Native Americans killing locals, the Mexican Republic decided to welcome Americans who wanted to settle in Texas by granting them the  title of “impresario.” Gradually, the American impresario population came to vastly outnumber the Tejano population of Mexican-born Texans, causing additional divisions in the region. 

At first, after Santa Anna was elected as president in 1833 after Farías left office, the Texans were given some power, as their representation in legislative matters was increased, but ultimately, Santa Anna dissolved Congress and pursued conservative policies,  making pro-federalist Texas even more upset. Fighting broke out in Mexico’s central and southern provinces during this period, but the rebels were quickly crushed.

The first shots of the Texas Revolution were fired in the Battle of Gonzales

The final spark for a revolution was lit on September 10, 1835, when a Mexican soldier stationed in  Texas fought with a citizen in Gonzales. Things boiled over quickly, and the citizens took up arms against the authorities. 

The Mexican force, which was facing a  disadvantage, ultimately retreated, bringing the first victory to the Texans. Even though no actual fighting erupted, the news of the encounter quickly spread all over Texas, uniting the people and motivating them to fight against Mexican rule. Not only that, but many volunteers also joined the revolution directly from the US by crossing the border.

The mobilization of the citizens throughout Texas eventually forced the Mexican Army out of the region, and they established a provisional government in its place called the Consultation – also known as the Texian Government. 

In December of 1835, Santa Anna assembled an army of about six thousand troops and embarked on an expedition toward Texas. On February 23, 1836, Santa Anna’s forces reached the small mission-turned-fort called the Alamo, which the Texans had captured.

Even though the garrison had received some minor reinforcements, Santa Anna’s troops were able to finally take the fort on March 6, losing between five hundred and six hundred men in the process. Almost all of the men stationed in the Alamo lost their lives. By this time, the Consultation had agreed on declaring independence from Mexico. 

Furthermore, the Texans managed to avenge their fallen brothers at the decisive Battle of San Jacinto, where about 900 Texans managed to defeat an army of about  1,350 Mexicans and captured 700, including Santa Anna. After weeks of negotiations, they set Santa  Anna free on June 1, 1836, and according to the Treaties of Velasco that Santa Anna signed, Mexico would remove troops from the region, establishing a new unofficial border with Texas. 

The Texas Revolution was one of the few successful rebellions against centralist-conservative Mexico.  With its secession, Mexico spun into yet another period of instability, even though it never actually recognized the independence of Texas. Tensions increased between Mexico and the United States as well. Mexico believed that Texas managed to win the war only due to the help received from the US even though the United States was never directly involved in the conflict. However, a significant portion of the Texan army indeed included American volunteers  – some of them even members of the US Army. 

Republic of Texas

The US, on the other hand, recognized independent Texas in 1837. At that time, the United States’ expansionist policy of  “Manifest Destiny” was starting to come to fruition, and many Americans were in favor of the annexation of Texas. By the time Secretary John Quincy Adams claimed Florida for the US and Spain gave up on its claims in Oregon, the expansionist mindset was already well-rooted in the minds of  Americans.

Take note that the US had also gained a huge amount of territory in the form of the  Louisiana Purchase just a few decades earlier. Later, with the Monroe Doctrine, the US  warned European powers not to colonize the continent or attempt to install puppet governments. 

The other nations of the continent, including Mexico, initially thought that the US might be heading towards an alliance with them, but incidents like the Texas Revolution soon disillusioned them.

The late 1820s and 1830s had seen a relative halt in the expansionist efforts on the western front. It was not until the mid-1840s that the term “Manifest Destiny”  entered the scene of US politics. Novel in the name – but not in its nature – the term described the divine right of the United States to expand. 

The Pastry War

Main Article – The Pastry War

Meanwhile, Santa Anna had redeemed himself after leading the Mexicans in a short war against the French, known as the Pastry War. After the war ended in 1839, the state of Yucatán, which was Texas-inspired, declared its independence and struggled to maintain it. Stimulated by an increase in tariffs caused by a failing economy, further internal instability, and public discontent, Mexico was ripe for a revolution. And so it happened during a military uprising in 1841.

Santa Anna swept in as the provisional president, ultimately transforming the country into another dictatorship for three years. With all these existing problems, the Mexican sentiment toward reconquering Texas and Yucatán was growing. With his official comeback at the head of Mexican politics, Santa Anna ordered his armies to carry out raids on Texas.  

While the Mexicans saw initial success in capturing San Antonio, the Texans, under the leadership of Sam Houston, responded,  bouncing back and driving the Mexican troops out. Santa Anna was devastated. This defeat was a humiliation. Infuriated by the defeat, Mexico underwent yet another revolt, deposing and forcing Santa Anna into exile in late 1844.

He would be back, though. The resentment toward the Texans had grown even more, which was stimulated by the fact that the United States was, in parallel, considering annexing the territory.  Insisting that Texas was still a part of Mexico, the Mexican government declared that its annexation would be a declaration of war.  

The Mexican government was desperate to take back its former territory, and after the election of the expansionist President James K. Polk in the US, the tense Mexican-American relations resulted in a war over the annexation of Texas. In response to the public upheaval, in late 1844, President John Tyler had drawn up a second treaty,  a joint resolution aimed at annexing Texas, which, unlike the first treaty, required only a majority of the House and the Senate to be passed.  

Eventually, the Senate passed the measure by a  razor-thin margin of twenty-seven to twenty-five. The major reservations stemmed from the fact that annexing Texas would lead to a conflict between Mexico and the United States, which it did. President Tyler signed the bill once the United States had voted for annexation – just days before Polk started his term. 

On December 29, 1845, Texas would officially become part of the Union. Polk fully understood that war was inevitable.  It can even be said that it was a part of his long-term plan, which originated back in his presidential campaign.

Hostilities erupted in April 1846 when a Mexican cavalry unit of 2,000 ambushed a 70-men US scouting force near Matamoros, killing 11 Americans and capturing more than 50. Word was sent to Polk, and just like that, the Mexican-American war was underway. is among the list of wars that are not relatively well-known despite their irrefutable importance.