The Mexican-American War, 1846–1848 – U.S. History (2024)

Chapter 11: A Nation on the Move: Westward Expansion, 1800–1860

Learning Objectives

By the end of this section, you will be able to:

  • Identify the causes of the Mexican-American War
  • Describe the outcomes of the war in 1848, especially the Mexican Cession
  • Describe the effect of the California Gold Rush on westward expansion

Tensions between the United States and Mexico rapidly deteriorated in the 1840s as American expansionists eagerly eyed Mexican land to the west, including the lush northern Mexican province of California. Indeed, in 1842, a U.S. naval fleet, incorrectly believing war had broken out, seized Monterey, California, a part of Mexico. Monterey was returned the next day, but the episode only added to the uneasiness with which Mexico viewed its northern neighbor. The forces of expansion, however, could not be contained, and American voters elected James Polk in 1844 because he promised to deliver more lands. President Polk fulfilled his promise by gaining Oregon and, most spectacularly, provoking a war with Mexico that ultimately fulfilled the wildest fantasies of expansionists. By 1848, the United States encompassed much of North America, a republic that stretched from the Atlantic to the Pacific.

JAMES K. POLK AND THE TRIUMPH OF EXPANSION

A fervent belief in expansion gripped the United States in the 1840s. In 1845, a New York newspaper editor, John O’Sullivan, introduced the concept of “manifest destiny” to describe the very popular idea of the special role of the United States in overspreading the continent—the divine right and duty of White Americans to seize and settle the American West, thus spreading Protestant, democratic values. In this climate of opinion, voters in 1844 elected James K. Polk, a slaveholder from Tennessee, because he vowed to annex Texas as a new slave state and take Oregon.

Annexing Oregon was an important objective for U.S. foreign policy because it appeared to be an area rich in commercial possibilities. Northerners favored U.S. control of Oregon because ports in the Pacific Northwest would be gateways for trade with Asia. Southerners hoped that, in exchange for their support of expansion into the northwest, northerners would not oppose plans for expansion into the southwest.

President Polk—whose campaign slogan in 1844 had been “Fifty-four forty or fight!”—asserted the United States’ right to gain full control of what was known as Oregon Country, from its southern border at 42° latitude (the current boundary with California) to its northern border at 54° 40′ latitude. According to an 1818 agreement, Great Britain and the United States held joint ownership of this territory, but the 1827 Treaty of Joint Occupation opened the land to settlement by both countries. Realizing that the British were not willing to cede all claims to the territory, Polk proposed the land be divided at 49° latitude (the current border between Washington and Canada). The British, however, denied U.S. claims to land north of the Columbia River (Oregon’s current northern border) (Figure 11.13). Indeed, the British foreign secretary refused even to relay Polk’s proposal to London. However, reports of the difficulty Great Britain would face defending Oregon in the event of a U.S. attack, combined with concerns over affairs at home and elsewhere in its empire, quickly changed the minds of the British, and in June 1846, Queen Victoria’s government agreed to a division at the forty-ninth parallel.

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In contrast to the diplomatic solution with Great Britain over Oregon, when it came to Mexico, Polk and the American people proved willing to use force to wrest more land for the United States. In keeping with voters’ expectations, President Polk set his sights on the Mexican state of California. After the mistaken capture of Monterey, negotiations about purchasing the port of San Francisco from Mexico broke off until September 1845. Then, following a revolt in California that left it divided in two, Polk attempted to purchase Upper California and New Mexico as well. These efforts went nowhere. The Mexican government, angered by U.S. actions, refused to recognize the independence of Texas.

Finally, after nearly a decade of public clamoring for the annexation of Texas, in December 1845 Polk officially agreed to the annexation of the former Mexican state, making the Lone Star Republic an additional slave state. Incensed that the United States had annexed Texas, however, the Mexican government refused to discuss the matter of selling land to the United States. Indeed, Mexico refused even to acknowledge Polk’s emissary, John Slidell, who had been sent to Mexico City to negotiate. Not to be deterred, Polk encouraged Thomas O. Larkin, the U.S. consul in Monterey, to assist any American settlers and anyCalifornios, the Mexican residents of the state, who wished to proclaim their independence from Mexico. By the end of 1845, having broken diplomatic ties with the United States over Texas and having grown alarmed by American actions in California, the Mexican government warily anticipated the next move. It did not have long to wait.

WAR WITH MEXICO, 1846–1848

Expansionistic fervor propelled the United States to war against Mexico in 1846. The United States had long argued that the Rio Grande was the border between Mexico and the United States, and at the end of the Texas war for independence Santa Anna had been pressured to agree. Mexico, however, refused to be bound by Santa Anna’s promises and insisted the border lay farther north, at the Nueces River (Figure 11.14). To set it at the Rio Grande would, in effect, allow the United States to control land it had never occupied. In Mexico’s eyes, therefore, President Polk violated its sovereign territory when he ordered U.S. troops into the disputed lands in 1846. From the Mexican perspective, it appeared the United States had invaded their nation.

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In January 1846, the U.S. force that was ordered to the banks of the Rio Grande to build a fort on the “American” side encountered a Mexican cavalry unit on patrol. Shots rang out, and sixteen U.S. soldiers were killed or wounded. Angrily declaring that Mexico “has invaded our territory and shed American blood upon American soil,” President Polk demanded the United States declare war on Mexico. On May 12, Congress obliged.

The small but vocal antislavery faction decried the decision to go to war, arguing that Polk had deliberately provoked hostilities so the United States could annex more slave territory. Illinois representative Abraham Lincoln and other members of Congress issued the “Spot Resolutions” in which they demanded to know the precise spot on U.S. soil where American blood had been spilled. Many Whigs also denounced the war. Democrats, however, supported Polk’s decision, and volunteers for the army came forward in droves from every part of the country except New England, the seat of abolitionist activity. Enthusiasm for the war was aided by the widely held belief that Mexico was a weak, impoverished country and that the Mexican people, perceived as ignorant, lazy, and controlled by a corrupt Roman Catholic clergy, would be easy to defeat. (Figure 11.15).

U.S. military strategy had three main objectives: 1) Take control of northern Mexico, including New Mexico; 2) seize California; and 3) capture Mexico City. General Zachary Taylor and his Army of the Center were assigned to accomplish the first goal, and with superior weapons they soon captured the Mexican city of Monterrey. Taylor quickly became a hero in the eyes of the American people, and Polk appointed him commander of all U.S. forces.

General Stephen Watts Kearny, commander of the Army of the West, accepted the surrender of Santa Fe, New Mexico, and moved on to take control of California, leaving Colonel Sterling Price in command. Despite Kearny’s assurances that New Mexicans need not fear for their lives or their property, the region’s residents rose in revolt in January 1847 in an effort to drive the Americans away. Although Price managed to put an end to the rebellion, tensions remained high.

Kearny, meanwhile, arrived in California to find it already in American hands through the joint efforts of California settlers, U.S. naval commander John D. Sloat, and John C. Fremont, a former army captain and son-in-law of Missouri senator Thomas Benton. Sloat, at anchor off the coast of Mazatlan, learned that war had begun and quickly set sail for California. He seized the town of Monterey in July 1846, less than a month after a group of American settlers led by William B. Ide had taken control of Sonoma and declared California a republic. A week after the fall of Monterey, the navy took San Francisco with no resistance. Although some Californios staged a short-lived rebellion in September 1846, many others submitted to the U.S. takeover. Thus Kearny had little to do other than take command of California as its governor.

Leading the Army of the South was General Winfield Scott. Both Taylor and Scott were potential competitors for the presidency, and believing—correctly—that whoever seized Mexico City would become a hero, Polk assigned Scott the campaign to avoid elevating the more popular Taylor, who was affectionately known as “Old Rough and Ready.”

Scott captured Veracruz in March 1847, and moving in a northwesterly direction from there (much as Spanish conquistador Hernán Cortés had done in 1519), he slowly closed in on the capital. Every step of the way was a hard-fought victory, however, and Mexican soldiers and civilians both fought bravely to save their land from the American invaders. Mexico City’s defenders, including young military cadets, fought to the end. According to legend, cadet Juan Escutia’s last act was to save the Mexican flag, and he leapt from the city’s walls with it wrapped around his body. On September 14, 1847, Scott entered Mexico City’s central plaza; the city had fallen (Figure 11.16). While Polk and other expansionists called for “all Mexico,” the Mexican government and the United States negotiated for peace in 1848, resulting in the Treaty of Guadalupe Hidalgo.

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The Treaty of Guadalupe Hidalgo, signed in February 1848, was a triumph for American expansionism under which Mexico ceded nearly half its land to the United States. TheMexican Cession, as the conquest of land west of the Rio Grande was called, included the current states of California, New Mexico, Arizona, Nevada, Utah, and portions of Colorado and Wyoming. Mexico also recognized the Rio Grande as the border with the United States. Mexican citizens in the ceded territory were promised U.S. citizenship in the future when the territories they were living in became states. In exchange, the United States agreed to assume $3.35 million worth of Mexican debts owed to U.S. citizens, paid Mexico $15 million for the loss of its land, and promised to guard the residents of the Mexican Cession from Native American raids.

As extensive as the Mexican Cession was, some argued the United States should not be satisfied until it had taken all of Mexico. Many who were opposed to this idea were southerners who, while desiring the annexation of more slave territory, did not want to make Mexico’s large mestizo (people of mixed Native American and European ancestry) population part of the United States. Others did not want to absorb a large group of Roman Catholics. These expansionists could not accept the idea of new U.S. territory filled with mixed-race, Catholic populations.

Click and Explore

Explore the U.S.-Mexican Warat PBS to read about life in the Mexican and U.S. armies during the war and to learn more about the various battles.

CALIFORNIA AND THE GOLD RUSH

The United States had no way of knowing that part of the land about to be ceded by Mexico had just become far more valuable than anyone could have imagined. On January 24, 1848, James Marshall discovered gold in the millrace of the sawmill he had built with his partner John Sutter on the south fork of California’sAmerican River. Word quickly spread, and within a few weeks all of Sutter’s employees had left to search for gold. When the news reached San Francisco, most of its inhabitants abandoned the town and headed for the American River. By the end of the year, thousands of California’s residents had gone north to the gold fields with visions of wealth dancing in their heads, and in 1849 thousands of people from around the world followed them (Figure 11.17). The Gold Rush had begun.

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The fantasy of instant wealth induced a mass exodus to California. Settlers in Oregon and Utah rushed to the American River. Easterners sailed around the southern tip of South America or to Panama’s Atlantic coast, where they crossed the Isthmus of Panama to the Pacific and booked ship’s passage for San Francisco. As California-bound vessels stopped in South American ports to take on food and fresh water, hundreds of Peruvians and Chileans streamed aboard. Easterners who could not afford to sail to California crossed the continent on foot, on horseback, or in wagons. Others journeyed from as far away as Hawaii and Europe. Chinese people came as well, adding to the polyglot population in the California boomtowns (Figure 11.18).

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Once in California, gathered in camps with names like Drunkard’s Bar, Angel’s Camp, Gouge Eye, and Whiskeytown, the “forty-niners” did not find wealth so easy to come by as they had first imagined. Although some were able to find gold by panning for it or shoveling soil from river bottoms into sieve-like contraptions called rockers, most did not. The placer gold, the gold that had been washed down the mountains into streams and rivers, was quickly exhausted, and what remained was deep below ground. Independent miners were supplanted by companies that could afford not only to purchase hydraulic mining technology but also to hire laborers to work the hills. The frustration of many a miner was expressed in the words of Sullivan Osborne. In 1857, Osborne wrote that he had arrived in California “full of high hopes and bright anticipations of the future” only to find his dreams “have long since perished.” Although $550 million worth of gold was found in California between 1849 and 1850, very little of it went to individuals.

Observers in the gold fields also reported abuse of Native Americans by miners. Some miners forced Native Americans to work their claims for them; others drove them off their lands, stole from them, and even murdered them. Foreigners were generally disliked, especially those from South America. The most despised, however, were the thousands of Chinese migrants. Eager to earn money to send to their families in Hong Kong and southern China, they quickly earned a reputation as frugal men and hard workers who routinely took over diggings others had abandoned as worthless and worked them until every scrap of gold had been found. Many American miners, often spendthrifts, resented their presence and discriminated against them, believing the Chinese, who represented about 8 percent of the nearly 300,000 who arrived, were depriving them of the opportunity to make a living.

Click and Explore

VisitThe Chinese in Californiato learn more about the experience of Chinese migrants who came to California in the Gold Rush era.

In 1850, California imposed a tax on foreign miners, and in 1858 it prohibited all immigration from China. Those Chinese who remained in the face of the growing hostility were often beaten and killed, and some Westerners made a sport of cutting off Chinese men’s queues, the long braids of hair worn down their backs (Figure 11.19). In 1882, Congress took up the power to restrict immigration by banning the further immigration of Chinese.

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As people flocked to California in 1849, the population of the new territory swelled from a few thousand to about 100,000. The new arrivals quickly organized themselves into communities, and the trappings of “civilized” life—stores, saloons, libraries, stage lines, and fraternal lodges—began to appear. Newspapers were established, and musicians, singers, and acting companies arrived to entertain the gold seekers. The epitome of these Gold Rush boomtowns was San Francisco, which counted only a few hundred residents in 1846 but by 1850 had reached a population of thirty-four thousand (Figure 11.20). So quickly did the territory grow that by 1850 California was ready to enter the Union as a state. When it sought admission, however, the issue of slavery expansion and sectional tensions emerged once again.

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The Mexican-American War, 1846–1848 – U.S. History (2024)

FAQs

The Mexican-American War, 1846–1848 – U.S. History? ›

Mexican-American War, war between the United States and Mexico (April 1846–February 1848) stemming from the United States' annexation of Texas in 1845 and from a dispute over whether Texas ended at the Nueces River (Mexican claim) or the Rio Grande (U.S. claim).

What was significant about the Mexican-American War 1846 1848 in American history? ›

It paved the way for so many other important events, from the expansion and dispossession of indigenous people, the California Gold Rush, and American Civil War. It added the states of California, Texas, New Mexico, Utah, Arizona, Nevada, and parts of Colorado and Wyoming to the United States.

What was a significant result of the Mexican-American War of 1846 to 1848? ›

Final answer: The significant result of the Mexican-American War of 1846-1848 was the United States experiencing increasing tension over the issue of slavery. The correct option is (c).

What was the Mexican-American War and why was it fought? ›

One of the causes of this war were the continued claims to Texas from both the United States and Mexican governments. Other reasons were claims against the Mexican government by American citizens for damages during the continuous Mexican Revolutions of the period and the U.S. desire to claim California.

Why did the US declare war on Mexico in 1848? ›

On May 12, 1846, the United States Senate voted 40 to 2 to go to war with Mexico. President James K. Polk had accused Mexican troops of having attacked Americans on U.S. soil, north of the Rio Grande. But Mexico claimed this land as its own territory and accused the American military of having invaded.

What was the most significant impact of the Mexican-American War on Mexico? ›

The treaty effectively halved the size of Mexico and doubled the territory of the United States. This territorial exchange had long-term effects on both nations. The war and treaty extended the United States to the Pacific Ocean, and provided a bounty of ports, minerals, and natural resources for a growing country.

What was the main goal of the U.S. in the U.S.-Mexican War? ›

Polk took advantage of the animosity between the two nations to advance a political agenda focused on Manifest Destiny (the belief that the U.S. was preordained to expand across the American continent to the Pacific Ocean), and he perceived a war with Mexico as an opportunity to further annex Mexican territory to the ...

What was the overall end result of the Mexican War of 1846 1848? ›

The war—in which U.S. forces were consistently victorious—resulted in the United States' acquisition of more than 500,000 square miles (1,300,000 square km) of Mexican territory extending westward from the Rio Grande to the Pacific Ocean.

What was a major outcome of the Mexican-American War? ›

A major outcome of the Mexican-American War was that the United States gained significant territory, an area known as the Mexican Cession, which included present-day states of California, New Mexico, Arizona, Nevada, Utah, and portions of Colorado and Wyoming under the Treaty of Guadalupe Hidalgo.

What is one reason the Americans won the Mexican-American War? ›

The U.S. had Superior Firepower

Artillery (cannons and mortars) was an important part of warfare in 1846. The Mexicans had decent artillery, including the legendary St. Patrick's Battalion, but the Americans had the best in the world at the time.

What were the three main causes of the Mexican-American War? ›

The Mexican-American War of 1846-1848 was a combination of Mexican unwillingness to recognize Texas independence, the desire of Texans for statehood, and American desire for westward expansion.

How did the Mexican-American War affect slavery? ›

The Mexican-American War reopened the slavery-extension issue, which divided the North and South and which had been largely dormant since the Missouri Compromise.

What happened to the Mexicans after the Mexican-American War? ›

The War ended with the signing of the Treaty of Guadalupe Hidalgo, which gave Mexican citizens one year to choose U.S. or Mexican citizenship. Approximately 115,000 people chose to remain in the U.S. and become citizens by conquest.

Why shouldn't the US have gone to war with Mexico in 1846? ›

This was called the Mexican American War. Alternatively known as, The Mexican War, Mexican Independence, or Mexican Cessation. The United States was unjustified in going into war with Mexico because President James K. Polk provoked it, the robbery of land, and the slavery expansion.

How did the Mexican-American War end? ›

The Treaty of Guadalupe Hidalgo, that brought an official end to the Mexican-American War (1846-1848), was signed on February 2, 1848, at Guadalupe Hidalgo, a city north of the capital where the Mexican government had fled with the advance of U.S. forces.

Why did Mexico lose the Mexican-American War? ›

In his 1885 memoirs, former U.S. President Ulysses Grant (himself a veteran of the Mexican war) attributed Mexico's defeat to the poor quality of their army, writing: "The Mexican army of that day was hardly an organization.

What was one significant result of the Mexican-American War? ›

What did the U.S. gain by winning the Mexican-American War? Under the Treaty of Guadalupe Hidalgo, which settled the Mexican-American War, the United States gained more than 500,000 square miles (1,300,000 square km) of land, expanding U.S. territory by about one-third.

What important U.S. history event happened in 1846? ›

September 21–24: Battle of Monterrey (Mexican–American War).
  • June 14 – Mexican–American War: The California Republic declares independence from Mexico.
  • June 15 – Bear Flag Revolt: American settlers in Sonoma, California start a rebellion against Mexico and proclaim the California Republic.

What was the significance of the Mexican Cession of 1848? ›

With the annexation of more than 525,000 square miles of land, the Treaty of Guadalupe Hidalgo extended the boundaries of the United States west to the Pacific Ocean. This agreement, along with the 1853 Gadsden Purchase, created the southern border of the present-day United States.

What effects did the Mexican War have in American politics from 1848 to 1850? ›

In this time of heightened sectional tensions, southerners believed that if one did not actively protect slavery and its expansion, one supported abolition. As a direct result of the Mexican Cession, the California Gold Rush began in 1849 which caused a massive frenzy to organize and admit California into the Union.

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