Mexican War Summary

  • Last updated on November 11, 2022

The United States, by the middle of the nineteenth century, had expanded its western frontier to the Mississippi River through purchases of territory from France and Spain. Many Americans, however, felt that the country had a manifest destiny to expand its horizons across the continent to the Pacific Ocean. Standing in the way of such an expansion was the even younger republic, the United Mexican States, which had achieved its independence from Spain in 1823.

The United States, by the middle of the nineteenth century, had expanded its western frontier to the Mississippi River through purchases of territory from France and Spain. Many Americans, however, felt that the country had a manifest destiny to expand its horizons across the continent to the Pacific Ocean. Standing in the way of such an expansion was the even younger republic, the United Mexican States, which had achieved its independence from Spain in 1823.

The Texas Revolution

At the invitation of the Mexican government, a substantial number of U.S. citizens had moved into Texas, setting up towns and ranches, often accompanied by their African slaves. In 1836, these Texan immigrants rebelled against their Mexican overlords. After defeats at the Alamo and Goliad, the Americans, under General Sam Houston, defeated the Mexican army of Antonio López de Santa Anna at San Jacinto, captured the Mexican leader following the battle, and forced him to acquiesce to their independence. However, they failed to establish a clear line of demarcation between Mexico and the new Texas Republic.

The U.S. government acceded to the wishes of the Texans and annexed their republic in 1845. The U.S. Congress declared Texas the twenty-eighth state in the Union on December 22, 1845. The Mexican government and people reacted negatively. Because General Santa Anna’s actions had been forced by the Texans, the Mexican government never officially recognized Texas as independent. The Mexicans were even more reluctant to accept Texas’s incorporation into the United States.

T<sc>ime</sc> L<sc>ine of the</sc> T<sc>exas</sc> R<sc>evolution and the</sc> M<sc>exican</sc> W<sc>ar</sc>June 30, 1835Texans seize Anahuac Garrison and the Texas Revolution begins.Feb. 23-Mar. 6, 1836Battle of the Alamo: Overpowering Mexican force led by General Antonio López de Santa Anna destroys the American defenders of the Alamo’s garrison.Apr. 21, 1836Battle of San Jacinto: General Sam Houston leads Texans in victory.Oct. 22, 1836Texans declare independence and elect Houston president.May 6, 1846Mexican War begins.May 8, 1846Battle of Palo Alto: General Zachary Taylor leads the American army to victory.May 9, 1846Battle of Resaca de la Palma.June 30, 1846-Jan. 13, 1847Occupation of California and the Southwest.Sept. 21–24, 1846Battle of Monterrey: Important conquest for the U.S. because Monterrey is a key site on the approach to Saltillo.Jan. 2, 1847Battle of Santa Clara, California.Jan. 8, 1847Battle of Rio San Gabriel (Los Angeles), California.Jan. 9, 1847Battle of La Mesa (Los Angeles), California.Feb. 22–23, 1847Battle of Buena Vista: The narrow U.S. victory secures the northern approaches to Mexico City.Mar., 1847Battle of Veracruz: Port city surrenders, and General Winfield Scott begins march toward Mexico City.Apr. 17–18, 1847Battle of Cerro Gordo: Defeat of Mexican army blocking the U.S. advance into central Mexico.Aug. 20, 1847Battle of Contreras: General Winfield Scott leads American troops in a crushing defeat of the Mexican army.Aug. 20, 1847Battle of Churubusco: Scott’s forces suffer heavy casualties, but Mexican army suffers overwhelming defeat.Sept. 8, 1847Battle of Molino del Rey.Sept. 12–13, 1847Siege of Chapultepec: Scott’s troops occupy Mexico City on Sept. 14., concluding the military stage of the war.Feb. 2, 1848Treaty of Guadalupe Hidalgo ends the war. The Mexican government cedes Texas, New Mexico, Arizona, and California to the United States.
Tensions with Mexico

President James K. Polk sought to solve the border problem and the acquisition of Texas by seeking to buy all the lands claimed by Mexico between the United States and the Pacific Ocean. He sent an emissary, John Slidell, to Mexico to negotiate with the government. The Mexican state had been politically chaotic since achieving its independence from Spain. General Mariano Paredes y Arrillaga, a fervent nationalist, refused to even receive the U.S. envoy. Thus the stage was set for a confrontation between the two countries.

President Polk struck first. He ordered General Zachary Taylor to lead an army into the disputed territory and take a stand at the Rio Grande, the southernmost point in the land claimed by the Americans. Mexican General Mariano Arista, commander of the Mexican troops at Matamoros, received his orders from Mexico City to attack the U.S. Army. On paper, the odds favored the Mexicans, who outnumbered the Americans, 3,700 men to 2,290. However, the Mexicans lacked modern artillery and were using ordinance that still shot cannonballs. The Americans, who had cannons of a much greater range, could fire explosive shells into the ranks of the Mexican infantry at little risk to themselves. This difference in weaponry, together with the fact that the Mexican army consisted of ill-equipped, ill-fed and poorly led draftees, led to convincing victories for the Americans under Taylor at Palo Alto (May 8, 1846) and the battles in Texas and northern Mexico that followed. In the Palo Alto battle, Taylor sustained only 9 killed, 44 wounded, and 2 missing. The Mexican forces at Palo Alto, and at the Resaca de la Palma battle (May 9) that followed shortly thereafter, lost more than 1,000 men, hundreds of prisoners, and huge quantities of war equipment and supplies.

General Zachary Taylor, commander of American forces in the Mexican War. (Library of Congress)

Antonio López de Santa Anna, commander of the Mexican armies and several times president of the country. (Library of Congress)

Mexican General Pedro de Ampudia had a force of approximately 10,000 troops to defend the major Mexican stronghold of Monterrey (September 20–24, 1846). The defenders manned a stone fortress known as the Black Fort, containing 400 defenders and a dozen guns, some of them eighteen pounders. They awaited Taylor’s attack on September 21, 1846. Taylor saw the city’s western defenses as the Mexican weak spot and sent 2,000 men under General William Worth on a detour around those points. When the Mexican cavalry rushed to attack the Americans, the U.S. artillery opened up, sending the Mexican horsemen back in disorder. Worth then cut off any supplies to the beleaguered city from the south. However, Mexican defenses within the city itself proved to be formidable. They poured heavy fire on the Americans from the windows of the city’s buildings. Taylor lost more than 400 men during a direct frontal assault on the city’s eastern positions. The next day, Worth, continuing his attack on the western sector, had more success. He took the major strongpoints there, turned captured guns on the retreating Mexicans, and took the pressure off Taylor’s troops in the east. The Americans advanced into the city, taking it street by street. On September 25, the Mexicans surrendered the city and marched out, leaving behind virtually all their artillery and ammunition as agreed to in the terms signed by Mexican general Ampudia. Taylor’s total casualties, dead and wounded, amounted to 453 men. Casualties suffered by Ampudia’s troops were considerably higher.

Invasion of Mexico

In addition to the armies of Taylor and Winfield Scott, President Polk directed those of General John E. Wool and General Stephen W. Kearny to move against Mexico. General Wool and his army had orders to invade Mexico’s center and join Taylor’s force at Buena Vista (February 22–23, 1847), where the two combined to defeat the self-styled “Napoleon of the West,” Santa Anna. The Mexican general had returned from exile following his loss of Texas some eleven years previously. Although the Mexican army acquitted itself well in this critical confrontation and appeared to be winning the battle, Santa Anna chose to retreat toward the capital rather than continue his engagement with Taylor.

Texas Revolution and the Mexican War

Polk ordered General Kearny to lead a force into New Mexico and ultimately to California to secure these Mexican outposts. Polk also expected Commodore John D. Sloat to support Kearny’s army by seizing California ports with Sloat’s Naval Pacific Squadron. First General Kearny marched nearly nine hundred miles from Fort Leavenworth, Kansas, and occupied Santa Fe without firing a shot. Once the U.S. flag flew over New Mexico, Kearny prepared to move farther west to the Pacific Coast. At the same time, Brevet Captain John C. Frémont marched into Northern California, at Sacramento. This invasion proved premature, for when Frémont discovered that Mexican general José Castro proposed to block his entry into California’s settled coastal area, he decamped and retreated to Oregon.

Meanwhile, Kearney had entered Southern California, and after some difficult negotiations and with the aid of the naval forces, he managed to secure control of the state through a treaty with the resident Californios, who did not identify with the government in Mexico City. Despite some sporadic skirmishing with the locals in the takeover, Kearney managed to secure California for the United States with little loss to the men under him. Frémont agreed to accept Kearny’s authority as well, thus ending his independent effort.

While the Mexicans had attempted to defend themselves from Taylor’s army in the north, other U.S. forces under General Scott landed at Veracruz in March, 1847. The Americans experienced only minor opposition before the port city surrendered. Scott then began the march toward Mexico City itself.

The Battle of Resaca de la Palma, the second major engagement of the Mexican War. (Institute of Texan Cultures)

In March, 1847, American ships bombarded the port city of Veracruz, preparing the way for General Zachary Taylor’s march on Mexico City. (Library of Congress)

The Mexican Defense

The Mexican defenders were led by General Santa Anna, fresh from his retreat following the battle at Buena Vista. He had a force of more than 20,000 men, double that of Scott’s. The two armies met at Cerro Gordo on April 18, 1847. Captain Robert E. Lee found a path around Santa Anna’s flank that led to a quick defeat of the Mexican forces. The Mexican general left the battlefield so precipitously that all his personal possessions—his silverware, official papers, money, even his dinner—fell into the hands of the Americans. Puebla, at that time Mexico’s second city, surrendered without a fight on May 15. The U.S. forces were only one hundred miles from the capital.

Santa Anna fell back to prepared positions around Mexico City itself. Again he failed to anticipate the moves of his opposition, and one of his commanders allowed himself to be surrounded. At the Battle of Contreras on August 20, American forces, led by Scott, inflicted a crushing defeat on the Mexican army. The Americans suffered only a few casualties, and the Mexicans lost 700 men and their best cannons. Also on August 20, at almost the same time, American forces attacked Churubusco. Scott’s forces also attacked at Molino del Rey (September 8). Scott’s desire to keep the pressure on a disorganized enemy cost him many casualties. At Churubusco alone, the Americans lost 137 killed, 879 wounded, and 40 missing in action. This list contained the worst casualties sustained by the invaders up to that time. Mexican losses were estimated at more than 2,000.

General Zachary Taylor at the siege of Monterrey, Mexico. (F. R. Niglutsch)

During the Churubusco battle, the Americans captured a group of Irish deserters from the U.S. Army who had switched allegiance to the Mexicans. Called the St. Patrick’s Battalion, the captured Irish received harsh treatment at the hands of the Americans. Most were later executed by the U.S. Army while the U.S. flag was raised over Chapultepec Castle.

The culminating battle of the Mexico City campaign centered on the storming of Chapultepec Castle on September 13, 1847. Among the defenders was a group of Mexican cadets, many of them children, who tried to fight off the Americans. Several threw themselves off the battlements wrapped in Mexican flags rather than surrender to the invaders. They are known in Mexico as “los niños héroes”—the child heros. Shortly after the castle fell, Mexican resistance in the capital for all intents and purposes ceased. Scott’s troops occupied Mexico City on September 14, 1847. The United States had won the war.

Faced with U.S. occupation of its capital city as well as a number of states along its northern border, the Mexican government was forced to sue for peace. In the treaty, signed at the Villa de Guadalupe in the small village of Guadalupe Hidalgo on February 2, 1848, the Mexican government ceded Texas, New Mexico, Arizona, and California to the United States in exchange for $15 million. The Rio Grande became the boundary between the two countries. The border line extended to the Pacific Ocean, ending approximately fifteen miles below the city of San Diego.

General Santa Anna died impoverished in his native state of Veracruz. General Taylor won election to the presidency of the United States in 1848, only to die little more than one year after taking office. General Scott ran for president in 1852 but was defeated by another Mexican War hero, General Franklin Pierce.

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