Expansion and the Mexican-American War

The Mexican–American War, 1846–1848

After the United States annexed Texas in 1845, border disputes led to war with Mexico in 1846.

Learning Objectives

Identify the causes of the Mexican–American War

Key Takeaways

Key Points

  • Conflict with Mexico began when the United States annexed Texas as a state in 1845.
  • Mexico claimed that the new border between Texas and Mexico was the Nueces River, while the United States contested the border was the Rio Grande.
  • Fighting began when a detachment of U.S. cavalry was attacked near the Rio Grande.
  • Zachary Taylor and Winfield Scott led armies to a series of military successes that culminated in the capture of Mexico City in 1847.

Key Terms

  • Treaties of Velasco: Documents signed in Texas on May 14, 1836, intended to conclude the hostilities between Texas and Mexico and recognize Texas’ independence; however, Mexico never ratified them.
  • annexation: The permanent acquisition and incorporation of a territorial entity into another geo-political entity (either adjacent or non-contiguous).

Background

The Mexican–American War was an armed conflict between the United States and Mexico that took place in 1846–1848. It occurred in the wake of the 1845 U.S. annexation of Texas, which Mexico considered part of its territory despite the 1836 Texas Revolution in which the Republic of Texas claimed its independence.

The border of Texas as an independent state had never been settled. The Republic of Texas claimed land up to the Rio Grande, based on the Treaties of Velasco. However, Mexico refused to accept these as valid, claiming the border was the Nueces River. U.S. President James Polk endorsed the Rio Grande boundary, which incited a dispute with Mexico.

After a series of failed negotiations with Mexico City, Polk ordered General Zachary Taylor and his forces south to the Rio Grande to enter the territory that Mexicans disputed. On April 25, 1846, a Mexican cavalry detachment routed the patrol, killing 16 U.S. soldiers. In response, Polk asked for a declaration of war. Congress declared war on Mexico on May 13, 1846, after only a few hours of debate.

The War

The US military strategy had three main objectives: 1) Take control of northern Mexico, including New Mexico; 2) seize California; and 3) capture Mexico City. The US War Department sent a cavalry force under General Stephen W. Kearny to invade western Mexico from Jefferson Barracks and Fort Leavenworth, reinforced by a Pacific fleet under John D. Sloat. This was done primarily because of concerns that Britain might also try to seize the area. Two more forces, one under John E. Wool and the other under Taylor, were ordered to occupy Mexico as far south as the city of Monterrey.

California, Kearny, and Sloat

US Army Captain John C. Frémont entered California in December 1845 and was slowly marching to Oregon when he received word that war between Mexico and the United States was imminent. On June 15, 1846, some 30 settlers staged a revolt and seized the small Mexican garrison in Sonoma, California. The republic was in existence scarcely more than a week before the U.S. Army, led by Frémont, took over on June 23.

Commodore John Drake Sloat, upon hearing of imminent war and the revolt in Sonoma, ordered his naval and marine forces to occupy Monterrey on July 7. On July 15, Sloat transferred his command to Commodore Robert F. Stockton who put Frémont’s forces under his orders. On July 19, upon receiving official word of the start of war, Frémont’s so-called California Battalion entered Monterrey in a joint operation with some of Stockton’s sailors and marines. The U.S. forces easily took over the north of California.

From Alta California, Mexican General José Castro and Governor Pío Pico fled southward. When Stockton’s forces stopped in San Pedro, Stockton sent 50 U.S. Marines ashore. This force entered Los Angeles unresisted on August 13, 1846. With the success of this “Siege of Los Angeles,” the nearly bloodless conquest of California seemed complete.

Meanwhile, General Kearny’s forces fought in the decisive Battle of Rio San Gabriel. The next day, January 9, 1847, the Americans fought and won the Battle of La Mesa. On January 12, the last significant body of Californios surrendered to U.S. forces. That marked the end of armed resistance in California, and the Treaty of Cahuenga was signed the next day, on January 13, 1847.

Taylor and Scott’s Legacies

Led by Taylor, 2,300 U.S. troops crossed the Rio Grande and headed toward the besieged city of Monterrey. The hard-fought Battle of Monterrey resulted in serious losses on both sides. U.S. soldiers were introduced to urban warfare for the first time and had to adjust their battle tactics accordingly. The Mexican forces under General Pedro de Ampudia eventually surrendered.

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Battle of Monterrey: General Zachary Taylor and the US army defeated the Mexican army during the Battle of Monterrey, lasting September 21–24, 1846.

On February 22, 1847, Santa Anna personally marched north to fight Taylor in the Battle of Buena Vista. Furious fighting ensued, during which the U.S. troops were nearly defeated but managed to cling to their entrenched position. Rather than reinforce Taylor’s army for a continued advance, Polk sent a second army under General Winfield Scott to begin an invasion of the Mexican heartland.

On March 9, 1847, Scott performed the first major amphibious landing in U.S. history in preparation for the Siege of Veracruz. Meanwhile, mortars and naval guns reduced the city walls. The effect of the extended barrage destroyed the will of the Mexican side to fight, and they surrendered the city after 12 days under siege.

Scott then advanced on Mexico City on August 7. The capital was laid open in a series of battles, culminating in the Battle of Chapultepec. On September 14, 1847, When Scott entered Mexico City’s central plaza the city had fallen. 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.

A painting depicting the Battle of Chapultapec.

Battle of Chapultapec: U.S. forces began their assault on Chapultapec, the main fort protecting Mexico City, on September 12, 1847, with an artillery barrage.

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U.S. Occupation of Mexico City: This 1851 painting by Carl Nebel shows the U.S. occupation of Mexico City, which began after US forces captured the city in September 1847.

Treaty of Guadalupe Hidalgo

The Treaty of Guadalupe Hidalgo, signed in February 1848, was a triumph for U.S. expansionism under which Mexico ceded nearly half its land. The Mexican 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 came to recognize 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 American Indian raids.

Victory in Mexico

American victory in the Mexican–American war yielded huge acquisition of land and increased domestic tensions over slavery.

Learning Objectives

Identify the territories that the United States acquired at the end of the Mexican–American War

Key Takeaways

Key Points

  • After the U.S. army occupied Mexico City, the Treaty of Guadalupe Hidalgo was negotiated and brought the war to an end. The treaty gave the United States control of Texas, established the border at the Rio Grande, and ceded other Mexican lands to the United States in the southwest.
  • In return, Mexico received $18,250,000—less than half the amount the United States tried to offer for the land before the opening of hostilities.
  • In the United States, increasingly divided by sectional rivalry, the war was a partisan issue and an essential element in the origins of the American Civil War. Most Whigs in the North and South opposed it, while most Democrats supported it.
  • Southern Democrats, animated by a popular belief in manifest destiny, supported the war in hopes of adding slave-owning territory to the South and avoiding being outnumbered by the faster-growing North.
  • Northern antislavery elements feared the rise of a slave power; Whigs generally wanted to strengthen the economy with industrialization, not expand it with more land.
  • The war was one of the most decisive events for the United States in the first half of the 19th century, serving as a milestone especially within the U.S. narrative of manifest destiny.

Key Terms

  • Treaty of Guadalupe Hidalgo: The peace accord, largely dictated by the United States to the interim government of a militarily occupied Mexico City, and that ended the Mexican–American War (1846–1848) on February 2, 1848.
  • Rio Grande: A river that flows from southwestern Colorado in the United States to the Gulf of Mexico.
  • Mexican Cession: A historical name for the region of the present day southwestern United States that was acquired in the Treaty of Guadalupe Hidalgo.

Treaty of Guadalupe Hidalgo

Outnumbered militarily, and with many of its large cities occupied, Mexico could not defend itself and was also faced with internal divisions. It had little choice but to make peace on any terms. The Treaty of Guadalupe Hidalgo was signed on February 2, 1848, by U.S. diplomat Nicholas Trist and Mexican plenipotentiary representatives Luis G. Cuevas, Bernardo Couto, and Miguel Atristain.

The treaty ended the war and gave the United States undisputed control of Texas, established the U.S.–Mexican border as the Rio Grande River, and ceded to the United States the present-day states of California, Nevada, Utah, New Mexico, most of Arizona and Colorado, and parts of Texas, Oklahoma, Kansas, and Wyoming. In return, Mexico received $18,250,000—less than half the amount the United States had attempted to offer for the land before the opening of hostilities—and the United States agreed to assume $3.25 million in debts that the Mexican government owed to U.S. citizens.

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Treaty of Guadalupe Hidalgo: The first page of the handwritten Treaty of Guadalupe Hidalgo, which ended the Mexican–American War.

Opposition to the Acquisition

The acquisition was a source of controversy, especially among U.S. politicians who had opposed the war from the outset. In the United States, increasingly divided by sectional rivalry, the war was a partisan issue and an essential element in the origins of the American Civil War. Most Whigs in the North and South opposed it, while most Democrats supported it. Southern Democrats, animated by a popular belief in manifest destiny, supported it in the hopes of adding slave-owning territory to the South and avoiding being outnumbered by the faster-growing North.

Northern antislavery elements feared the rise of a slave power; Whigs generally wanted to strengthen the economy with industrialization, not expand it with more land. John Quincy Adams in Massachusetts argued that the war with Mexico would add new slavery territory to the nation. Northern abolitionists attacked the war as an attempt by slave-owners to strengthen the grip of slavery and thus ensure their continued influence in the federal government. Democratic Congressman David Wilmot introduced the Wilmot Proviso, which aimed to prohibit slavery in new territory acquired from Mexico. Wilmot’s proposal did not pass Congress, but it spurred further hostility between the factions.

Those who advocated for the war, in contrast, viewed the territories of New Mexico and California as only nominally Mexican possessions with very tenuous ties to Mexico. They saw the territories as actually unsettled (despite their large populations of American Indians), ungoverned, and unprotected frontier lands. The non-indigenous population there, where there was any at all, represented a substantial—in places even a majority—Anglo-American component. Moreover, the territories were feared to be under imminent threat of acquisition by the United States’ rival, the British.

Impact of the War

Manifest Destiny

The acquired lands west of the Rio Grande are traditionally called the Mexican Cession in the United States, as opposed to the Texas Annexation 2 years earlier. Mexico never recognized the independence of Texas prior to the war, and did not cede its claim to territory north of the Rio Grande or Gila River until this treaty.

While the Mexican–American War marked a significant point for the nation as a growing military power, it also served as a milestone especially within the U.S. narrative of manifest destiny. The resultant territorial gains set in motion many of the defining trends in U.S. 19th-century history, particularly for the American West. In doing much to extend the nation from coast to coast, the Mexican–American War was one step in the massive westward migrations of Americans, which culminated in transcontinental railroads and the Indian wars later in the same century.

The Politics of Slavery

The 1848 treaty with Mexico was one of the most decisive events for the United States. in the first half of the 19th century. However, it did not bring the United States domestic peace. Instead, the acquisition of new territory revived and intensified the debate over the future of slavery in the western territories, widening the growing division between the North and South and leading to the creation of new single-issue parties. Westward expansion of the institution of slavery took an increasingly central and heated theme in national debates preceding the American Civil War. Increasingly, the South came to regard itself as under attack by radical northern abolitionists, and many northerners began to speak ominously of a southern drive to dominate U.S. politics for the purpose of protecting slaveholders’ human property. As tensions mounted and both sides hurled accusations, national unity frayed. Compromise became nearly impossible and antagonistic sectional rivalries replaced the idea of a unified, democratic republic.

The suggestion that slavery be barred from the Mexican Cession caused a split within the Democratic Party. The 1840s were a particularly active time in the creation and reorganization of political parties and constituencies, mainly because of discontent with the positions of the mainstream Whig and Democratic parties in regard to slavery and its extension into the territories. The first new party was the small and politically weak Liberty Party, founded in 1840. This was a single-issue party made up of abolitionists who fervently believed slavery was evil and should be ended, and that this was best accomplished by political means. In 1848, many northern Democrats united with anti-slavery Whigs and former members of the Liberty Party to create the Free-Soil Party. The party took as its slogan “Free Soil, Free Speech, Free Labor, and Free Men,” and had one real goal—oppose extension of slavery into the territories.

The California Gold Rush

The discovery of gold in California in 1848 sent hundreds of thousands of people West in search of fortunes.

Learning Objectives

Examine the demographics of the population that participated in the California Gold Rush

Key Takeaways

Key Points

  • The California Gold Rush began on January 24, 1848, when James W. Marshall found gold at Sutter’s Mill in Coloma, California.
  • The gold-seekers, known as “forty-niners” (in reference to the year 1849), came from across the United States as well as from Latin America, Europe, Australia, and China.
  • Although $550 million worth of gold was found in California between 1849 and 1850, very little of it went to individuals.
  • Gold was first gathered using simple techniques such as panning, but as more people arrived, more expensive infrastructure was needed for mining.
  • As people flocked to California in 1849, the population of the new territory swelled from a few thousand to about 100,000, and boom towns like San Francisco formed nearly overnight.
  • The Gold Rush also had significantly negative effects on American Indians in the area, who were attacked and pushed off their lands.

Key Terms

  • boom town: A community that experiences sudden and rapid growth.
  • panning: A form of traditional mining that extracts gold from a placer deposit.
  • forty-niner: A miner who took part in the California Gold Rush of the mid-19th century.

Seeking Fortune in the West

The California Gold Rush began on January 24, 1848, when James W. Marshall found gold at Sutter’s Mill in Coloma, California. The first people to hear confirmed information of the gold rush were in Oregon, the Sandwich Islands (Hawaii), and Latin America, and were the first to start flocking to the state in late 1848. The news of gold eventually brought some 300,000 people to California from the rest of the United States and abroad. Approximately half of those arrived by sea, while half came from the east overland on the California Trail and the Gila River Trail.

The gold-seekers, known as “forty-niners” (in reference to the year 1849), often faced substantial hardships on their trip. While most of the newly arrived were Americans, the Gold Rush attracted tens of thousands from Latin America, Europe, Australia, and China. At first, the gold nuggets could be picked up off the ground. Later, gold was recovered from streams and riverbeds using simple techniques, such as panning. More sophisticated methods were developed and later adopted elsewhere. At its peak, technological advances reached a point where significant financing was required, decreasing the ratio of individual miners to gold companies. Although $550 million worth of gold was found in California between 1849 and 1850, very little of it went to individuals. While it led to great wealth for a few, many returned home with little more than they had when they started.

Effects of the Gold Rush

The effects of the Gold Rush were substantial. As people flocked to California in 1849, the population of the new territory swelled from a few thousand to about 100,000. San Francisco grew from a small settlement of about 200 residents in 1846 to a boomtown of about 36,000 by 1852. Roads, churches, schools, and new towns were built throughout California. The new arrivals quickly organized themselves into communities, and the trappings of “civilized” life—stores, saloons, libraries, stagelines, and fraternal lodges—began to appear. Newspapers were established, and musicians, singers, and acting companies arrived to entertain the gold-seekers. In 1849 a state constitution was written, a governor and legislature chosen, and California became a state as part of the Compromise of 1850.

New methods of transportation developed as steamships came into regular service. By 1869, railroads were built across the country from California to the eastern United States. Agriculture and ranching expanded throughout the state to meet the needs of the settler-invaders. At the beginning of the Gold Rush, there was no law regarding property rights in the goldfields, and a system of “staking claims” was subsequently developed.

The Gold Rush also had significantly negative effects on American Indians in the area, who were attacked and pushed off their lands. Observers in the gold fields reported abuse of American Indians by miners. Some miners forced American Indians to work their claims for them, while others drove them off their lands, stole from them, and even murdered them. Non-Americans 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% of the nearly 300,000 who arrived, were depriving them of the opportunity to make a living.

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Forty-Niner: A forty-niner, so called because he came to California in 1849, pans for gold.