Less than 50 years after its birth, the newborn Mexican republic of the 19th century faced its greatest threat for survival: a war with the United States. At the same time, less than 100 years after its own foundation, the promising young nation of the United States faced a crucial opportunity that would require great sacrifices. Lasting from 1846 to 1848, the Mexican-American War was a deeply consequential event in the history of both nations. In the case of Mexico, its defeat sent the nation into spiraling chaos, while in the case of the United States, the war signified an opportunity for expansion and consolidation as a major power both in the Americas and the world. The Mexican-American War was and still is a controversial and sensitive topic in both Mexico and the United States. Nevertheless, it is also a fundamentally consequential and interesting affair, filled with nuance and open to more discovery.
1. The War Resulted in Mexico Losing More than Half of its Territory
Before the war officially started between the US and Mexico, the latter nation was busy fighting rebellions throughout its vast territory and dealing with crippling political divisions. Out of all the chaos, several crucial blows were dealt to the newly-independent nation. One of them was the Texas Revolution and its fight for sovereignty. Originally part of Mexico, the territory became populated by American settlers and immigrants. Eventually, their struggle for autonomy from a distant and largely ineffective authority was born. In 1835, the Texans rebelled; in 1842, they repelled a Mexican attempt to retake the land, and in 1845, they were finally annexed by the United States.
Texas’ rebellion and annexation by the United States were the catalysts for a larger, bloodier conflict. It was also the first major loss of Mexican territory in its northern border, one that eventually led to losing more than half of its sovereign land. This was well within America’s expansionist wishes. The recently-elected president, James K. Polk, had made his intentions clear, hoping to expand the US further into the west, settling Oregon, California, and Texas. His position was a continuation of the Manifest Destiny doctrine that dominated the American political psyche of the 19th century.
Some describe the Mexican-American War as unjust and predatory on the US’ part, especially considering how weak the Mexican nation was. Nevertheless, the territories captured by the Americans were largely neglected by the Mexican central government and were never truly a priority. Furthermore, the lands claimed by both countries were first inhabited and claimed by Native Americans and indigenous populations, who themselves frequently fought both the US and Mexico, seeing their claims as illegitimate. By the end, the United States had annexed what is today Arizona, California, Colorado, Nevada, New Mexico, Utah, and Wyoming.
2. The War Was a Training Ground for Future American Leaders
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The Mexican-American War was a deeply consequential conflict for a multitude of reasons, from those that are more historically significative, like the expansion of the US, to those that were smaller yet, in proportion, equally transformative, like the sudden changes in the lives of thousands of Mexicans living in what became new American territories. But one often overlooked effect of the war was the involvement of numerous future leaders and public figures, namely, several men who would play a significant role during the American Civil War.
Besides American leaders who already had significant power during the Mexican-American War, like General Winfield Scott, figures like future general and president Ulysses S. Grant, as well as George Meade and George B. McClellan, would participate in the war well before becoming leaders of the Union Army. Others, like future Generals Robert E. Lee, Thomas J. “Stonewall” Jackson, Braxton Bragg, and George Pickett, would go on to fight for the Confederacy. And sure, others would not participate in the battles during the war with Mexico but were, regardless, on their journey towards greater leadership roles, like then congressman from Illinois and future president of the United States, Abraham Lincoln.
The Mexican-American War was a formative experience for all the aforementioned men. In the case of Ulysses S. Grant, for example, the war served him as a real-life military training ground, where he learned to command troops and gained combat experience, something impossible to obtain in the academy. At the same time, the war affected Grant well beyond his military abilities, forming him in his general leadership and politics. Grant famously wrote about the war that he was “bitterly opposed to the measure” and considered it ”the most unjust ever waged by a stronger [nation] against a weaker nation.”
3. The War Faced Opposition in the United States
Although, at the time, American politics were dominated by expansionism, led by the doctrine of Manifest Destiny and mainly carried out against Native Americans and their lands, the consensus for a war with Mexico was not absolute. There were numerous detractors, and the conflict faced party-line division. The Democratic Party, led by President James K. Polk, supported the war, while the Whig Party, which controlled the House of Representatives, was opposed to the conflict, going as far as censoring the US President for waging what they called an “unnecessary” and “unconstitutional” war.
Nevertheless, when it came to a vote, both the Senate and the House voted almost unanimously to go to war with Mexico. The Whigs voted in favor of war despite their doubts and opposition to the conflict. They believed that a lack of support behind the war would mean political Armageddon for their party, similar to what happened to the Federalists in the War of 1812. Opposition to the war was not exclusive to the Whigs; some Democrats were also against it. The southern Democratic senator and slavery advocate, John C. Calhoun, opposed the war as he feared the annexation of new territory would stir up discussion about slavery and lead to more anti-slavery legislation being passed.
Perhaps the most adamant detractor was the freshman congressman from Illinois, Abraham Lincoln. In his “Spot Resolutions” presented to Congress, Lincoln made his case against the war. He asked for eight resolutions to be passed, investigating whether the war had truly been initiated as detailed by President Polk. The resolutions were never adopted or even truly considered by Congress; instead, Lincoln was largely ignored, and Polk insisted that he waged a just war.
4. An Irish Battalion Deserted the US Army: Los San Patricios
At the beginning of the Mexican-American War, a group of European immigrants, primarily Irish, deserted the American Army and joined the Mexican side, forming a sort of Foreign Legion. They were called the Saint Patrick’s Battalion, owing their name to the Irish Patron Saint, but they were commonly referred to as San Patricios. Though made up mainly of Irishmen who had left their country because of the Irish Potato Famine, there were also other nationalities. Most, if not all, were Catholic, sharing the faith with the Mexicans, which is, perhaps, one of the reasons why they joined their side.
Many reasons are given to suggest why the San Patricios deserted the US Army, and though it is impossible to say with absolute certainty what inspired all of the men to change sides, including those who were not Irish, the letters of their leader John Riley and several field entries by senior officers point towards their true motivations: a shared Catholic faith, sympathy for the Mexican cause, and their defense against an unjust war. Also, a motivating reason was better financial compensation, which for poor immigrants was certainly important.
The Americans heavily punished the San Patricios for treason. All in all, some 50 San Patricios were officially executed by the US Army. During the last offensive of the war, at the Battle of Chapultepec, 30 San Patricios were hanged by order of General Scott. He had instructed Colonel William Harney to hang the men at the precise moment when the American flag was raised at the Chapultepec Castle, with the San Patricios having full view of the Mexican defeat. The San Patricios continue to be remembered in Mexico, being officially commemorated every September 12 but also celebrated each Saint Patrick’s Day.
5. Los Niños Heroes: The Six Cadets Who Refused Defeat
At the same battle where 30 of the San Patricios were hanged, a different legend was born. When the Americans reached Mexico City, the Mexican army prepared one last defense. General Winfield Scott led the American offensive, while the controversial Mexican figure, General Antonio Lopez de Santa Anna, led the defense. The Mexicans had control of Chapultepec Castle, a strategic location that the US Army wanted to capture before attacking Mexico City. The Mexican defeat at Chapultepec gave way for the Americans to capture the capital and win the war.
It was there, at the last major defense by Mexico, that a group of six military cadets gave their lives and became a myth within the collective Mexican imagery. The San Blas Battalion stood at the feet of the castle but was defeated by the US Army after having been severely weakened by bombardment for two days. When the Americans advanced and reached the castle, they were welcomed by enemy fire from the Mexican cadets. They had been called for the battle as there were no other reserves, and the castle was the home of their academy, el Colegio Militar. They, however, posed no real threat to the experienced and numerous American troops, who defeated them quickly and soundly.
Nevertheless, before the Americans got hold of the Mexican flag and raised their own, the legend of Los Niños Heroes tells that one of the cadets took the Mexican flag, wrapped himself with it, and jumped from the heights of the castle so that no US soldier would defile the national symbol. Although the legend remains a powerful national myth in Mexico, it is generally known that the tale is largely untrue, as the flag was captured by the Americans and then returned to Mexico many decades later.