Manifest Destiny’s Cost: The Mexican-American War

A historical depiction of the Mexican-American War.

From 1846 to 1848, Mexico and the United States fought each other in a controversial and bloody war in order to decide the border between the two countries. This war was the culmination of decades of deep-rooted political animosity between Mexico and America, which was fostered by America’s ideology of Manifest Destiny—the belief that the United States was destined by God to expand across the world. While the war achieved its objectives of acquiring a vast amount of territory from Mexico, which included California, Nevada, Utah, New Mexico, and Wyoming, it furthered tensions between the North and South. 

Background

The start of the Mexican-American War roots back to 1821, more than two decades before the war started. At that time, Mexico was a wealthy and vast country that stretched from Guatemala to present-day Oregon. The southern parts of Mexico were densely populated, but Mexico’s northern territory, including present-day Texas, was sparsely populated. In order to solve this issue, the Mexican government encouraged American settlers, especially farmers, to move into Texas, as the land in Texas was both fertile and expansive. However, the Mexican government would soon come to regret this decision.

First, Mexican and American settlers clashed heavily in both culture and political views. For example, American settlers were mostly Protestant and supported slavery, whereas Mexico was a Catholic nation that abolished and heavily frowned upon slavery. These differences caused immediate tensions, and these tensions were further amplified when many American settlers disregarded Mexican laws and authority. 

The tensions between Mexican citizens and American settlers soon reached a boiling point in the 1830s, and it marked the beginning of the Texas Revolution, as Texan settlers sought independence from the Mexican government.  The most famous of the battles during the Texas Revolution was the Battle of the Alamo, a key fight that took place from February 23 to March 6, 1836, in San Antonio, Texas. A small Texan force, including David Crockeet, was ambushed by a much larger Mexican force led by General Santa Anna. Despite a valiant standoff from Texan forces, they succumbed after just 13 days, and almost all of the defenders—including children and women—were slaughtered. 

Another important battle of the Texas Revolution was the Battle of San Jacinto, which was fought on April 21, 1836. This battle occurred after a series of defeats for Texan forces, which motivated Texan soldiers to win in memory of these losses. This battle, shockingly lasting only 18 minutes, was led by General Sam Houston against General Antonio Lopez de Santa Anna. The Texan forces won when Sam Houston’s army launched a surprise attack on the Mexican camp during their afternoon siesta, which is a short afternoon nap traditionally taken in Mexican culture. These soldiers were motivated by the Battle of Alamo, and they shouted "Remember the Alamo! Remember Goliad!” as they ambushed Mexican forces. 

After numerous battles, Texas declared itself an independent republic in 1836. While the United States acknowledged Texas’ independence, Mexico refused to do so and considered Texas as a rebellious territory rather than a sovereign nation.

For the next nine years after Texas’ independence, the Republic of Texas sought to join the United States. This issue became a hot topic of debate within America, as Southern states supported annexing Texas because they saw it as an opportunity to expand slavery and increase their influence in Congress, whereas Northern states feared that it would give Southern States too much power. This debate over Texas’ annexation prevented Texas from being admitted for nearly a decade, and it worsened tensions between the North and South as well.

This hesitation was broken down when President James Polk was elected in 1845, as he was a strong supporter of Manifest Destiny. Therefore, he immediately annexed Texas after his inauguration, which officially made Texas the United States’ 28th state. However, Mexico was outraged by this action because they never saw Texas as an independent state, and they threatened war against the United States for this. At the same time, Polk hoped to buy California and other territories in the West from Mexico for 25 million dollars, but Mexico refused. 

Polk, seeing this as an act of disrespect, sent American troops to the disputed region between the Nueces River and the Rio Grande River, which was claimed by both the U.S. and Mexico. There, he deliberately tried to provoke a conflict to justify war and America’s territorial expansion. 

Polk’s plan succeeded, and in May 1846, shots were fired, and American soldiers were killed in a small fight near the Rio Grande. Polk used this skirmish as a justification to declare war on Mexico, as they had invaded American territory and shed American blood. Thus, the Mexican-American War began.

The War

The Mexican-American war wasn’t universally supported. There were many critics, among those Abraham Lincoln, who questioned Polk’s motives and challenged the legitimacy of the conflict. Famously, Lincoln created “Spot Resolutions,” which were a series of inquiries presented that questioned the specific location—the “spot”—where American blood was first shed in order to challenge Polk’s claim. Furthermore, many Northerners viewed the war as an aggressive and unjust attempt to expand slavery and the political power of Southern States. 

Despite the protests from different groups, the U.S. military campaign was swift and successful, as American forces captured key territories in California and the Southwest, and they eventually even occupied Mexico City. This pressured the Mexican government into cooperating with the United States, and in 1848, they acquiesced. The war officially ended with the signing of the Treaty of Guadalupe-Hidalgo, which stated that Mexico would recognize the Rio Grande as the official border of Texas, and that they would cede a large amount of territory to the United States. These lands, formally known as the Mexican Cession, included present-day California, Nevada, Utah, and parts of around six other states. In compensation, the United States would give Mexico $15 million.

Aftermath

A map of all of the land the U.S. gained as a result of the Mexican Cession in 1848.

The consequences of the Mexican-American war were immense. For the United States, the war was mostly beneficial because it meant that the dream of Manifest Destiny was fulfilled, as America was able to gain access to the Pacific Ocean. Furthermore, California, a state acquired in the Mexican Cession, would soon become an important economic hub following the Gold Rush of 1849. However, over 13,000 Americans were killed during the war, and the acquisition of these lands further reignited the national debate over slavery, as the United States couldn’t decide if these new states would allow slavery or not. 

In Mexico, meanwhile, the war was a horrifying national tragedy, since they had lost upwards of 25,000 people, nearly half of their territory, and suffered from political instability for many years. A lot of Mexicans viewed this war as a humiliating surrender and a painful reminder of their country’s losses, impacting decades of trade between Mexico and the U.S. 

In conclusion, the Mexican-American War was a pivotal episode in American history. It was driven by the ambition of expansion, fueled by political and cultural differences, and marked by controversy and dissent. While it achieved the goal of expanding U.S. territory and fulfilling the vision of Manifest Destiny, it also exposed the deep divisions within the United States and set the stage for future conflicts over slavery and national identity. The war's legacy continues to shape the histories of both nations and serves as a scary reminder about the costs of imperial ambition.

In the grand scheme of international affairs and battle, the Mexican-American war may just seem like a blip in existence. However, it was the start of many important events that impacted the United States and foreign countries. This war wasn't just a territorial struggle; it was the turning point that set the stage for the Civil War and redefined America’s role on the global stage.