Introduction
The Mexican-American War was a pivotal chapter in North American history, characterized by a complex interplay of historical events and factors. It emerged against the backdrop of the 1820 Mexican Revolution, a significant precursor to the conflict, which had already sown the seeds of discontent and calls for sovereignty in Mexico. The annexation of Texas following the Texan Revolution further exacerbated tensions between the nations. This contentious act led to a volatile dispute over the border's boundary, where the Rio Grande and Nueces River symbolized the competing claims. At the helm of these tumultuous events were influential political figures such as President James K. Polk, who championed an aggressive expansionist agenda, and the resilient and sometimes controversial leadership of Mexico's Antonio López de Santa Anna. These political leaders, military figures like Generals Zachary Taylor and Stephen W. Kearny, and Commodore Matthew Perry played pivotal roles in shaping the trajectory. The Mexican-American War was the crucial moment that shaped North America's map and political dynamics.
Causes and Road to War
The 1820 Mexican Revolution
The 1820 Mexican Revolution, often known as the "Plan of Iguala," played a central role in Mexico's journey toward independence from Spanish colonial rule. Leaders like Agustín de Iturbide and Vicente Guerrero catalyzed this revolutionary movement through political, social, and economic discontent in New Spain (Mexico). As Spain faced challenges in Europe, it was compelled to make concessions. The "Plan of Iguala" declared Mexican independence, emphasizing religious freedom, unity among Mexicans of different backgrounds, and the establishment of a constitutional monarchy. Uniting Creole and indigenous populations marked a significant shift in the fight for Mexican independence that ultimately led to Spanish rule ending in 1821.
General D. Antonio Lopez De Santa-Anna, president of the Republic of Mexico Library of Congress, Washington D.C. (reproduction no. LC-USZ62-21276)[1]
Antonio López de Santa Anna:
Antonio López de Santa Anna became a dominant presence in Mexican politics and a symbol of Mexican independence and its tumultuous leadership during the 19th century. His multifaceted career included overseeing the garrison at Veracruz during the Mexican independence and later serving as Mexico's president on numerous occasions. Santa Anna's legacy is characterized by early support for independence and later authoritarian rule, marked by shifting alliances and centralized power. His influence significantly shaped Mexican history [i]during the turbulent periods of the Texas Revolution and the Mexican-American War and stirred the Mexican nation to fight the U.S.
Annexation of Texas:
The annexation of Texas by the United States in 1845 was a momentous event in American history that sparked significant tension. Having gained independence from Mexico in 1836, Texas sought to join the United States due to economic challenges and a desire for territorial expansion. The annexation was driven by various factors, including Manifest Destiny, which advocated westward expansion. However, this move faced opposition as it raised the divisive issue of slavery expansion, further dividing the North and South. President James K. Polk's support led to the completion of Texas' annexation, making it by one vote the 28th state of the United States in December 1845 and intensifying the tensions that would culminate in the Mexican-American War.
Border Dispute:
A contentious border dispute between the United States and Mexico emerged. It centered on where the border between the two nations should lie. Initially, ambiguity shrouded the exact boundary, but two primary contenders emerged: the Rio Grande, favored by the United States based on the 1819 Adams-Onís Treaty, and the Nueces River, asserted by Mexico. This dispute was fueled by Mexico's desire to retain control of Texas and the United States' expansionist ambitions following Texas' annexation. The conflicting claims to the Rio Grande and the Nueces River created a volatile situation along the border (seen below in the map), leading to clashes between U.S. troops and Mexican forces. These tensions ultimately erupted in the Mexican-American War in 1846, emblematic of broader territory, sovereignty, and American expansionism issues.
Disputed Territory [2]
Diplomatic tensions played a significant role in the lead-up to the Mexican-American War. One key factor was the failure of negotiations between the United States and Mexico to resolve their territorial disputes. Mexico was unwilling to accept the U.S. annexation of Texas in 1845 and saw it as a violation of their sovereignty, which had long been a source of tension. Efforts to negotiate a peaceful settlement regarding the Texas border and other territorial issues were fruitless, as Mexico refused to recognize the Rio Grande as the legitimate border. At the same time, the U.S. insisted on its claim. This diplomatic impasse heightened the prospects of military conflict as it became increasingly clear that a peaceful resolution was unlikely.
Additionally, U.S. President James K. Polk's aggressive policies and expansionist agenda further exacerbated tensions. Andrew Jackson “’ Old Hickory’ took him under his wing, so Polk became known as ‘Young Hickory’”3 Polk continued Jackson's belief of a strong border as was a proponent of Manifest Destiny, believing that the United States was destined to expand across the continent. His administration was determined to acquire Mexican territories in California and New Mexico, and his expansionist policies were evident in his willingness to use force if necessary to achieve these goals. This stance was apparent in his decision to dispatch troops under General Zachary Taylor to the disputed border region between the Nueces River and the Rio Grande, effectively instigating a military confrontation with Mexican forces. He also dispatched Frémont and Carlson to California to incite rebellion against the Mexican government in 1845-1846. This expedition had scientific and political purposes, including surveying and mapping the territory and assessing its potential for U.S. expansion. These aggressive actions and Polk's desire to acquire Mexican lands heightened hostilities, ultimately leading to the outbreak of the Mexican-American War in 1846.
Major Battles and Campaigns
Glynn, Charles R. Battle of Palo Alto, 8th May. [1846] Map. https://www.loc.gov/item/2001622060/.4
Palo Alto (May 8, 1846) and B. Resaca de la Palma (May 9, 1846) battles marked the beginning of the Mexican-American War. General Zachary Taylor, leading U.S. forces, clashed with Mexican troops under General Mariano Arista near the Rio Grande as part of the border dispute. At Palo Alto (battle map from 1846 above), American artillery and infantry faced Mexican cavalry and artillery in a significant engagement, where Taylor's effective use of artillery proved pivotal. The Battle of Resaca de la Palma happened the next day. The U.S. forces managed to outflank the Mexicans, leading to a Mexican retreat. These battles highlighted the effectiveness of U.S. military tactics and technology and demonstrated the escalating tensions on the border.
Following the victories at Palo Alto and Resaca de la Palma, General Zachary Taylor's U.S. forces occupied the Mexican city of Matamoros (May 18, 1846). This occupation was strategically crucial as Matamoros was a critical supply and transportation hub for Mexican forces. It marked a significant advancement for the U.S. in the early stages of the war, giving them a foothold on Mexican soil and the ability to control vital logistical routes for future military operations.
After initial skirmishes, the U.S. Army, still led by General Zachary Taylor, laid siege to the city of Monterrey (September 21-24, 1846), a significant Mexican stronghold in northeastern Mexico. The siege lasted for several days and resulted in intense urban combat. Under General Pedro de Ampudia, the Mexican forces surrendered to the U.S. Army, granting the United States control of an essential northern city and further destabilizing Mexican positions in the region.
Battle of Buena Vista (February 22-23, 1847) was a significant U.S. victory and further demonstrated the prowess of American forces. U.S. forces, commanded by General Zachary Taylor, faced Mexican troops led by General Antonio López de Santa Anna. The battle took place in the mountainous terrain near Buena Vista, and it was characterized by intense fighting, with Santa Anna launching multiple attacks. Despite being heavily outnumbered, Taylor's forces managed to hold their ground and repel the Mexican assaults.
On March 9, 1847, General Scott and Commodore Perry achieved the first successful amphibious landing in U.S. history at Veracruz, Mexico. Over the following months, between March and September, Scott steadily advanced toward Mexico City. Even though his progress may not have met the swiftness desired by President Polk, shortly after the success at Veracruz, he voiced his determined perspective to Buchanan, declaring, "'I differ with you in opinion,' he asserted, 'I would not only march to the City of Mexico, but would pursue Santa Anna's Army wherever it was, and capture and destroy it.'"5
The capture of Mexico City (September 8-15, 1847) came six months later and was the decisive battle in the Mexican-American War. After a series of battles and engagements throughout the war, including the Battle of Chapultepec on September 13, 1847, where U.S. forces overcame strong Mexican defenses, American forces, under the command of General Winfield Scott, entered Mexico City on September 14, 1847. The occupation of the capital was a turning point, and it forced the Mexican government to negotiate a peace settlement, which led to the Treaty of Guadalupe Hidalgo. The capture of Mexico City marked the end of major hostilities in the war. It solidified the United States' territorial gains, which included present-day California, New Mexico, and other southwestern territories.
The signing on February 2, 1948, of the Treaty of Guadalupe Hidalgo marked the official end of the Mexican-American War and had significant consequences for the United States and Mexico. The treaty resulted in Mexico's substantial cession of territory to the United States. Mexico ceded vast land, including present-day California, New Mexico, Arizona, Nevada, Utah, and parts of Colorado, Wyoming, Kansas, and Oklahoma. This acquisition of territory, often referred to as the Mexican Cession, dramatically expanded the territorial boundaries of the United States and played a crucial role in shaping the nation's geographic and economic development.
In return for the cession of these territories, the United States agreed to compensate Mexico with $15 million, a significant sum at the time, but still half of what they were willing to pay before the war. The compensation, often viewed as reparations, aimed to alleviate some financial burdens on Mexico resulting from the war. It is important to note that the treaty also included provisions recognizing the property rights of Mexican citizens in the ceded territories and allowing those inhabitants to become U.S. citizens if they chose to do so. While the Treaty of Guadalupe Hidalgo brought an end to the hostilities between the two nations, it also left a legacy of contentious issues, including questions of land rights and the treatment of Mexican Americans in the newly acquired territories.
Consequences
The consequences of the Mexican-American War were multifaceted and far-reaching. One of the most immediate outcomes was U.S. territorial expansion. The acquisition of vast swaths of land in 1848, known as the Mexican Cession, significantly increased the size of the United States. This expansion paved the way for the westward migration of Americans, the development of the transcontinental railroad, and the discovery of valuable resources like gold in California, ultimately shaping the nation's economic and demographic landscape.
The war also stirred discontent and resistance in Mexico. The loss of nearly half of its territory to the United States was a profound blow to Mexican national pride and sovereignty. It contributed to political instability and internal strife in Mexico as various factions and leaders contested the legitimacy of the Mexican government. Additionally, the war exacerbated economic hardships and social inequality, further fueling discontent among the Mexican population. The consequences of the conflict continued to influence Mexican politics and society for decades, leaving a legacy of territorial loss and national humiliation that remained a source of contention and historical memory in Mexico.
The Mexican-American War sparked intense debates in the United States over its morality and impact on the nation. It was a divisive issue, particularly concerning whether the war was just and necessary or an act of aggression driven by expansionist aims. Prominent figures like Henry David Thoreau and Abraham Lincoln criticized the war, and it played a pivotal role in the broader debate over the expansion of slavery into newly acquired territories. This debate culminated in the Wilmot Proviso, which sought to prohibit slavery in the Mexican Cession, highlighting the deep-rooted tensions between the North and the South and foreshadowing the sectional conflicts that would eventually lead to the American Civil War.
There were lasting effects on U.S.-Mexico relations. The war engendered a deep sense of resentment in Mexico, and it would be many years before diplomatic relations normalized between the two countries. The border disputes and territorial losses also sowed the seeds of future conflicts and disputes, as the border region remained a source of tension and disagreement. Furthermore, the war underscored the power disparity between the two nations, contributing to distrust in U.S.-Mexico relations. The legacy of the war continues to influence the bilateral relationship to this day, impacting issues such as trade, immigration, and security cooperation between the two neighboring nations.
Finally, the Mexican-American War served as a critical training ground for several influential leaders of the American Civil War, among them Robert E. Lee, George Pickett, Thomas "Stonewall" Jackson, Ulysses S. Grant, and George Meade. Their experiences during this conflict gave them valuable insights and skills that would later shape their roles in the American Civil War. Lee's tactical acumen, Pickett's battlefield experience, Jackson's resilience, Grant's determination, and Meade's leadership all found their roots in the crucible of Mexico, where they honed their military abilities and leadership styles before becoming central figures in the more significant conflict that loomed on the horizon.
Footnotes
General D. Antonio Lopez De Santa-Anna, president of the Republic of Mexico Library of Congress, Washington D.C. (reproduction no. LC-USZ62-21276)
“Gateway South: The Campaign for Monterrey,” US Army, March 15, 2006, https://history.army.mil/brochures/the%20campaign%20for%20monterrey/the%20campaign%20for%20monterrey.htm, Map- Mexican American War.
David A. Clary, Eagles and Empire: The United States, Mexico, and the Struggle for a Continent (New York: Bantam Dell, 2009), 63.
Glynn, Charles R. Battle of Palo Alto, 8th May. [1846] Map. https://www.loc.gov/item/2001622060/.
Robert W. Merry, A Country of Vast Designs: James K. Polk, the Mexican War and the Conquest of the American Continent (New York, NY: Simon & Schuster, 2009), 352.
Bibliography
Clary, David A. Eagles and Empire: The United States, Mexico, and the struggle for a continent. New York, NY: Bantam Dell, 2009. “Gateway South: The Campaign for Monterrey.” US Army, March 15, 2006. https://history.army.mil/brochures/the%20campaign%20for%20monterrey/the%20campaign%20for%20monterrey.htm.
General D. Antonio Lopez De Santa-Anna, president of the Republic of Mexico. [c1847] Library of Congress, Washington D.C. (reproduction no. LC-USZ62-21276). https://www.loc.gov/pictures/item/2004669619/ Glynn, Charles R. Battle of Palo Alto, 8th May. [1846] Map. https://www.loc.gov/item/2001622060/.
Merry, Robert W. A country of vast designs: James K. Polk, the Mexican War and the conquest of the American continent. New York, NY: Simon & Schuster, 2009.
Millett, Allan Reed, and Peter Maslowski. For the Common Defense: A military history of the United States of America from the Revolutionary War through today. New York, NY: Free Press, 2012.
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