# 14.2: The Mexican-American War


In the days after the election of 1844 before Polk’s inauguration, at the behest of lame duck President Tyler, Congress passed a resolution to annex Texas. Although Mexico had finally recognized Texas’s independence in 1845, it held that the border between Mexico and Texas was the Nueces River, as it had been from the colonial era. Texas—and now the United States—held the border as the Rio Grande. The area between the two rivers was not the real point of contention for the two countries. The Rio Grande wanders aimlessly for hundreds of miles far into New Mexico and presentday Colorado; in effect, claiming the Rio Grande as the boundary tacitly laid claim to hundreds of thousands more acres. Mexico responded to annexation by cutting off diplomatic relations with the U.S.; both countries prepared for war. As a last-ditch effort to avoid war, Polk sent emissary John Slidell to Mexico City to resolve the border dispute. His secondary mission, however, was to secure California and New Mexico for the United States. Slidell was authorized to pay $5 million for New Mexico and as much as$25 million for Alta (Upper) California. Soon after Slidell’s arrival in Mexico City, the Mexican press learned of his mission to attempt buying so much Mexican territory. Newspapers and journals denounced Slidell and the United States, and leaflets appeared all over the city threatening rebellion if the government negotiated. Slidell was sent away.

Polk seized this opportunity to provoke war with Mexico. He ordered General Zachary Taylor into the disputed territory between the rivers. When a skirmish broke out between Taylor and the Mexican general assigned to patrol the disputed territory, Polk declared war, saying that he had tried every effort at reconciliation. “Mexico,” he stated, “has passed the boundary of United States, invaded our territory, and shed American blood upon the American soil.” Despite opposition from some Whigs, most notably Abraham Lincoln, Congress overwhelmingly approved the declaration of war. The view from Mexico City was very different, however. Mexico contended that the United States had not only taken Texas, but also tried to double Texas’s size. Moreover, when Mexico tried to defend its territory, the United States claimed that Mexico had invaded U.S. land.

The U.S. strategy for the Mexican-American War called for a three-pronged attack on Mexico. The Army of the West was to take and occupy New Mexico; the Army of the Center, to remain in northern Mexico. In anticipation of war with Mexico, the United States assembled a Navy fleet off the coast of California, deploying Marines to the ships. In June of 1846, a small group of mostly American settlers seized the garrison at Sonoma, California. The takeover was peaceable; in fact, no shots were fired. Many of the settlers and californios, or Mexican residents of California, supported the rebellion, as the government of the California territory was ineffectual and notoriously unstable: in the twenty-five year period before the revolt, leadership had changed hands more than forty times. Upon taking the garrison, the rebels proclaimed a new government of the California Republic. This Republic was very short-lived, lasting less than a month; indeed, few Californians knew of its existence. Twenty-six days after the birth of the California Republic, an army corps of engineers under the command of John Frémont marched into Sonoma. The Republic disbanded, and Frémont and the U.S. took over.

Meanwhile, the third prong of the U.S. attack on Mexico, the Army of Occupation, was to take Mexico City. General Winfield Scott led an amphibious assault against the port city of Veracruz and, after taking the city, began his march to the capitol. Scott’s arrival in Mexico coincided with great political turmoil in the nation; in the time since the outbreak of war, the Mexican president had been overthrown by a general. The general then tried to abrogate the constitution, declare martial law, and take power himself; consequently, he was overthrown in a rebellion. The army then invited Santa Anna back from exile to resume the presidency. By the time that Scott took Veracruz, Santa Anna had only just arrived and taken command.

Scott’s army was successful in taking much of the city. On August 20, Scott asked for surrender from Santa Anna; Santa Anna agreed to negotiate. Rather than seriously negotiating surrender, however, Santa Anna used the time to shore up the city defenses. By the time the armistice was at an end, Santa Anna was ready for battle, with his forces concentrated at Chapultepec Castle at the center of the city. The defenders of the Castle, about 1,000 men and the cadets from the military academy, laid land mines all over slopes of the steep hill upon which the Castle was located. The land mines failed to explode. After a fierce battle, Scott’s forces prevailed. Mexican sources attest that by the time Scott’s forces reached the Castle, only a handful of cadets remained to defend it. After the death of his comrades, the last remaining cadet wrapped himself in the Mexican flag and jumped from the palace terrace, plummeting to his death on the steep rocks below.

## Treaty of Guadalupe Hidalgo and the Aftermath of the War

The Treaty of Guadalupe Hidalgo, which ended Mexican-American War, was signed in February of 1848. The treaty confirmed the U.S. title to Texas and ceded the Alta California and New Mexico territories to the United States, some 525,000 square miles. Mexico was allowed to keep everything south of the Rio Grande. The United States agreed to pay $15 million and to assume the claims of Americans against the Mexican government, about$3,250,000. In short, Mexico lost more than half of its territorial landmass in the Treaty of Guadalupe Hidalgo. The land ceded to the United States eventually became the states, or part of the states, of California, Arizona, New Mexico, Texas, Utah, Nevada, Colorado, Wyoming, and Kansas, tremendously increasing the U.S. holdings and stoking the fires of Manifest Destiny. The most radical adherents of Manifest Destiny had gone so far as to demand the annexation of not only “all of Texas,” but all of Mexico as well. Why, given the expansionist climate of the era, did the United States not lay claim to all of Mexico? Perhaps the best answer to this question lies in an examination of the problems that arose from the Mexican Cession itself.

Through the Treaty of Guadalupe Hidalgo, the United States acquired about 55% of Mexico. Of course these lands were not “empty” but (sparsely) populated with indigenous peoples and Mexican citizens who suddenly, and through no choice of their own, found themselves residents of the United States. It is estimated that there were 80,000 Mexican citizens in California in the late 1840s. Many of the families had been residents of the California or New Mexico territories for generations, since the Spanish colonial period. Mexico was keenly interested in ensuring that these Mexicans would be provided for under the Treaty of Guadalupe Hidalgo, which stated that all Mexican citizens who remained in the ceded lands for more than one year could become naturalized U.S. citizens. Moreover, the original version of the treaty guaranteed that Mexican and Spanish land deeds and grants would be recognized by the United States, allowing resident Mexicans to retain ownership of their lands. Later amendments and interpretations of the treaty weakened this provision.

However, racial tensions emerged as the conquest of the territories of the Cession set a pattern for violence and racial antagonism that still resonates today. Over the next decades, Mexicans and Mexican-Americans alike (some having become citizens, some having declined the offer and remaining Mexican citizens) lost their lands as Texas, California, New Mexico, and the United States government itself declared the Mexican and Spanish land deeds “imperfect,” questioned their veracity, and ultimately took the lands of tejanos, californios, and others. Before the Treaty of Guadalupe Hidalgo, Mexicans owned all lands valued over $10,000 in California; by the 1870s, they owned only one-quarter of these lands; by the 1880s, californios were relatively landless. Thousands went from being landowners to laborers, sometimes on the very land they had once owned. Much of the work was migratory in nature, and Mexican laborers were paid as much as two-thirds less than white laborers. California, Texas, and other soon-to-be states also passed laws that targeted and politically unempowered Mexican-Americans. A good example of this type of legislation was California’s Greaser Act, enacted in 1885. Technically, the Greaser Act was an antivagrancy law. However, “vagrants” were defined in the law as “all persons who are commonly known as ‘Greasers,’ or the issue of Spanish and Indian blood…and who go armed and are not peaceable and quiet persons.” In general, Hispanics became more and more alienated from the dominant society in the decades after Guadalupe Hidalgo. So why didn’t the United States acquire “all of Mexico” after conquering Mexico City? Some historians argue that racism played a large role. It was one thing to take the thinly-populated portions of Mexico that could be populated with many more Caucasian Americans and another thing entirely to take over a country, or “uncontrolled dominion,” with a turbulent history, populated with people of mixed ancestry, whom many Americans considered to be “mongrels.” Ultimately, Mexico would have been an expensive, complicated problem for the United States. In taking the California and New Mexico territories, the U.S. increased its land mass by some 20% and gained the important ports of San Diego and San Francisco, thus allowing for trade with Asia, a much more pragmatic and manageable arrangement. Because the Mexican Cession delineated by the Treaty of Guadalupe Hidalgo represented a tremendous increase to the land mass of the United States, it did much to further manifest destiny. The last major territorial acquisition of the continental United States followed on the heels of the Mexican Cession of 1848. In 1854, the United States and the Mexican government, once again under the control of the corrupt Santa Anna, signed the Mesilla Treaty, confirming the Gadsden Purchase. The United States paid$10 million for Arizona’s Mesilla Valley, approximately 30,000 acres. The purchase also clarified and finalized the border between the United States and Mexico. The U.S. desired this land for two additional reasons. First, the Mesilla Valley offered the best terrain for building a transcontinental railroad along a deep southern route. Second, by securing the land south of the Gila River, the United States finalized the border between California and Baja California (now the U.S. and Mexico) as south of the San Diego Bay, offering an excellent harbor. Plans were made for building the trans-continental railroad from Texas to San Diego, but nothing ever materialized.

The war was a tremendous military victory for the United States. The American military gained much experience. West Point and the Naval Academy claimed that their training were the key to success and justified their existence with the war’s success. The Marines won prestige as well and still sing of the conquest of “the halls of Montezuma.” The British and foreign skeptics also reevaluated their opinion on American military strength in the war’s aftermath. However, the war was also costly. Some 13,000 Americans died, most from disease. The war’s monetary cost was about \$100,000,000. The war also influenced foreign relations in Latin America, especially with Mexico, in lasting ways. Mexico, and much of Latin America, considered that the United States had deliberately provoked the war and that American greed was its primary underlying cause. The war intensified what has been referred to as “Yankeephobia” in Latin America, leading to distrust and suspicion. The United States, many contended, was untrustworthy, considered itself superior to others, and was a bully. It was called the “Colossus of the North.” Perhaps most significantly, the war upset the carefully-maintained domestic political truce over slavery. Some felt that the war would lead to a severe sectional crisis; poet Ralph Waldo Emerson observed, “Mexico will poison us!” Many Whigs opposed the war on principle, believing that the U.S. had no legal right to the land south of the Nueces River, the original boundary dispute between Texas and Mexico; many abolitionists believed that the war was provoked by the South in order to expand slavery. The sheer amount of possible slaveholding territory coming into the Union upset the balance established by the Missouri Compromise, reignited the slavery debate, and threatened stability. In response to this, Congressman David Wilmot introduced a bill, called the Wilmot Proviso, which would have banned slavery in any territory acquired from Mexico in the war. The measure was eventually defeated and never became law. However, it was strongly supported by representatives of Congress from the free states. Ultimately, the Mexican War represented the looming question of slavery’s future.

### Technological Development and Manifest Destiny

As the United States expanded geographically, it also underwent a period of growth and development in technology. Many advocates of manifest destiny saw a clear link between territorial growth and technological development; internal development, the mechanism that would spread American influence, followed on the heels of expansion. Two technologies were particularly important in facilitating communication and travel across the great distances from coast to coast: the telegraph and the railroad.

The development of a railroad infrastructure had begun in the 1830s in a limited area and proved to be viable and profitable. Rail travel transformed the American economy in the 1840s and 1850s, linking port cities to the interior. Before the advent of rail, the main route of commerce was along canal lines, which remained rail’s biggest competitor for quite some time. Although the steam locomotive was faster, shipping costs were cheaper by canal. By the 1850s, however, the railroad network had grown into the dominant means of transport by far. The growth of the telegraph and railroads also provided stability to the growing nation. The United States had become so big that critics doubted its ability to effectively govern so much land and so many people. Railroads and the telegraph provided one solution. Moreover, they facilitated the emergence of a national market system.

The expansion of railroads and the telegraph was not just an effect of manifest destiny. It was a continuation of an ongoing discussion in the American government: the debate over internal improvements. The issue was first raised under Jefferson and focused on the building of canals to better connect the trans-Appalachian frontier to the United States. The debate changed with evolving technology and was raised again and again, most notably during the Madison and Jackson presidencies. A constant in the debate was the discussion of whether or not it was appropriate to use federal money to fund these internal improvements. Manifest destiny and its accompanying technological advances was simply the latest incarnation of this debate.

The significance of these technological advances to the concept of Manifest Destiny appears in various cultural artifacts. In John Gast’s “American Progress” (1872), for example, the floating figure above the landscape resembles an angel and symbolizes the American belief that Manifest Destiny was divinely ordained. How does the angel express the concept of Manifest Destiny as espoused by John O’Sullivan? The paragraph below is from a nineteenth century description of the painting by George Crofutt, who widely distributed his engraving of it.

In “American Progress,” a diaphanously and precariously-clad America floats westward through the air with the “Star of Empire” on her forehead. She has left the cities of the east behind, and the wide Mississippi, and still her course is westward. In her right hand she carries a school book— testimonial of the national enlightenment, while with her left she trails the slender wires of the telegraph that will bind the nation. Fleeing her approach are Indians, buffalo, wild horses, bears, and other game, disappearing into the storm and waves of the Pacific coast. They flee the ponderous vision— the star “is too much for them.”

Technology enabled American expansionism throughout the North American continent by facilitating travel and communication. Americans were not the only ones to harness this technological power towards an expansionist goal; during the 1800s, these technologies further enabled European powers such as France, Britain, and Germany to establish a new kind of colonialism: imperialism. The telegraph and railroad, along with other new technologies such as the steamboat and the Maxim gun, one of the first machine guns, allowed a small number of Europeans to dominate large areas and great numbers of people and fuel their own Industrial Revolutions. In this way, Manifest Destiny became a part of a greater nineteenth century movement in expansionism.

## Summary

In 1845, the United States annexed Texas and admitted it to the Union. Tensions arose between the U.S. and Mexico over the boundary; the U.S. claimed the Rio Grande as the border, with Mexico claiming the long-established boundary at the Nueces River. The real reason for this border dispute was deeply linked to the expansionist desires of the United States; establishing the Rio Grande as the border would lay claim to a substantial portion of Mexico outside of the confines of Texas. John Slidell’s mission to Mexico exemplifies this intent; although his formal mission was diplomatic, he was secretly charged with buying a substantial portion of the Mexican northwest for the United States. When Mexicans responded to this offer with outrage, Polk took advantage by provoking war. The Mexican-American War, fought from 1846 to 1848, culminated with General Winfield Scott’s invasion of Mexico City.

The Treaty of Guadalupe Hidalgo ended the Mexican-American War. The treaty confirmed the U.S. title to Texas and ceded the Alta California and New Mexico territories to the United States, some 525,000 square miles. Mexico lost more than half of its territorial land mass. This ceded land eventually became all of, or part of, the U.S. states of California, Arizona, New Mexico, Texas, Utah, Nevada, Colorado, Wyoming, and Kansas, tremendously increasing U.S. holdings and stoking the fires of Manifest Destiny. In 1848, the Gadsden Purchase finalized the present border between the United States and Mexico with the purchase of Arizona’s Mesilla Valley.

The incorporation of so much Mexican territory and so many Mexican citizens into the United States led to great problems. The conquest of the territories of the Mexican Cession set a pattern for violence and racial antagonism that still resonates today. Over the next decades, Mexicans and Mexican-Americans alike lost their lands in Texas, California, and New Mexico; the United States government declared the Mexican and Spanish land deeds “imperfect,” questioning their veracity and ultimately taking the lands of tejanos, californios, and others.

The Mexican-American War adversely and lastingly influenced foreign relations in Latin America. Mexico, and much of Latin America, believed that the United States deliberately provoked the war, with American greed being its primary underlying cause. The war intensified Latin American “Yankeephobia,” leading to distrust and suspicion. The war also upset the carefully-maintained domestic political truce over slavery. Some felt that the war would lead to a severe sectional crisis. The sheer amount of potential slaveholding territory coming into the Union upset the balance established by the Missouri Compromise, reignited the slavery debate, and threatened stability.

Finally, the growth of technologies such as the telegraph and the railroad accompanied and enhanced the growth of Manifest Destiny, connecting the burgeoning country in communication and ease of travel. Rail linked the ports and the interior, facilitating trade and propelling the emergence of a national market system.

##### Exercise $$\PageIndex{1}$$

The “Greaser Act” is an example of

1. a law that targeted and politically unempowered Mexican-Americans.
2. “Yankeephobia” in Mexico.
3. an attempt to maintain the balance between free and slaveholding states in the aftermath of the Mexican-American War.
4. an attempt to settle territorial disputes between the United States and Mexico.

a

##### Exercise $$\PageIndex{2}$$

The Wilmot Proviso is an example of

1. a law that targeted and politically unempowered Mexican-Americans.
2. “Yankeephobia” in Mexico.
3. an attempt to maintain the balance between free and slaveholding states in the aftermath of the Mexican-American War.
4. an attempt to settle territorial disputes between the United States and Mexico.

c

##### Exercise $$\PageIndex{3}$$

As a result of the Treaty of Guadalupe Hidalgo, Mexico lost more than half of its territorial land mass.

1. True
2. False

a

##### Exercise $$\PageIndex{4}$$

The growth of rail and telegraph was hailed by expansionists as a means to

2. enhance internal development.
4. all of the above.

d

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