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The Mexican War

The Mexican War between the United States and Mexico began with a Mexican attack on American troops along the southern border of Texas on Apr. 25, 1846. Fighting ended when U.S. Gen. Winfield Scott occupied Mexico City on Sept. 14, 1847; a few months later a peace treaty was signed (Feb. 2, 1848) at Guadalupe Hidalgo. In addition to recognizing the U.S. annexation of Texas defeated Mexico ceded California and , New Mexico (including all the present-day states of the Southwest) to the United States.


As with all major events, historical interpretations concerning the causes of the Mexican War vary. Simply stated, a dictatorial Centralist government in Mexico began the war because of the U.S. annexation (1845) of Texas, which Mexico continued to claim despite the establishment of the independent republic of Texas 10 years before. Some historians have argued, however, that the United States provoked the war by annexing Texas and, more deliberately, by stationing an army at the mouth of the Rio Grande. Another, related, interpretation maintains that the administration of U.S. President James K. Polk forced Mexico to war in order to seize California and the Southwest. A minority believes the war arose simply out of Mexico's failure to pay claims for losses sustained by U.S. citizens during the Mexican War of Independence.

Mexican Politics

At the time of the war, Mexico had a highly unstable government. The federal constitution of 1824 had been abrogated in 1835 and replaced by a centralized dictatorship. Two diametrically opposed factions had arisen: the Federalists, who supported a constitutional democracy; and the Centralists, who supported an autocratic government under a monarch or dictator. Various clashing parties of Centralists were in control of the government from 1835 to December 1844. During that time numerous rebellions and insurgencies occurred within Mexican territory, including the temporary disaffection of California and the Texas Revolution, which resulted in the independence (1836) of Texas.

In December 1844 a coalition of moderates and Federalists forced the dictator Antonio Lopez de Santa Anna into exile and installed Jose Joaquin Herrera as acting president of Mexico. The victory was a short-lived, uneasy one. Although Santa Anna himself was in Cuba, other Centralists began planning the overthrow of Herrera, and the U.S. annexation of Texas in 1845 provided them with a jingoistic cause.

U.S. Policy

The U.S. annexation of Texas, by a joint congressional resolution (Feb. 27-28, 1845), had caused considerable political debate in the United States. The desire of the Texas Republic to join the United States had been blocked for several years by antislavery forces, who feared that several new slave states would be created from the Texas territory. The principal factor that led the administration of John Tyler to take action was British interest in independent Texas. Indeed, anti-British feeling lay behind most of the expansionist policy statements of the United States in this period. James Polk won the 1844 presidential election by advocating a belligerent stand against Britain on the Oregon Question. Once in office he declared that "the people of this continent alone have the right to decide their own destiny." About the same time the term Manifest Destiny came into vogue to describe what was regarded as a God-given right to expand U.S. territory. The term was applied particularly to the Oregon dispute, but it had relevance also to California, where American settlers warned of British intrigues to take control, and to Texas.

The Mexican Response and the Slidell Mission

As early as August 1843, Santa Anna's government had informed the United States that it would "consider equivalent to a declaration of war . . . the passage of an act for the incorporation of Texas." The government of Herrera did not take this militant position. It had already initiated steps, encouraged by the British, to recognize the independence of the Republic of Texas, and although Santa Anna's lame-duck minister in Washington broke diplomatic relations with the U.S. government immediately after annexation, in August 1845 the Herrera government indicated willingness to resume relations. Not only was the Herrera government prepared to accept the loss of Texas, but it also hoped to lay to rest the claims question that had plagued U.S.-Mexican affairs since 1825. Britain and France had used force, or the threat of it, to induce the Mexican government to pay their claims on behalf of their citizens. The United States, however, preferred to negotiate, and the negotiations had dragged on interminably.

Fearing that American patience was running short, Herrera seemed determined to settle the issue. He requested that the United States send a minister plenipotentiary to Mexico, and President Polk appointed John Slidell.

Slidell's authority, however, may have exceeded Herrera's intentions. Slidell was authorized to purchase California and New Mexico from Mexico and to settle the Texas boundary, which was a source of dispute even with the Mexican moderates. While the Republic of Texas had claimed the Rio Grande as its boundary, the adjacent Mexican state of Tamaulipas claimed the area north of the Rio Grande to the Nueces River.

By the time Slidell arrived in Mexico in December 1845, the Herrera government was under intense fire from the Centralists for its moderate foreign policies. The Centralist strategy was to appeal to Mexican national pride as a means of ousting Herrera. During August 1845 their leader, Mariano Parades y Arrillaga, began to demand an attack on the United States. When Slidell arrived, Herrera, in an effort to save his government, refused to meet with him. A few days later (December 14), Parades issued a revolutionary manifesto; he entered Mexico City at the head of an army on Jan. 2, 1846. Herrera fled, and Parades, who assumed the presidency on January 4, ordered Slidell out of Mexico.

After the failure of the Slidell mission, Polk ordered Zachary Taylor to move his army to the mouth of the Rio Grande and to prepare to defend Texas from invasion. Taylor did so, arriving at the Rio Grande on Mar. 28, 1846. Abolitionists in the United States, who had opposed the annexation of Texas as a slave state, claimed that the move to the Rio Grande was a hostile and aggressive act by Polk to provoke a war with Mexico to add new slave territory to the United States.

Whatever Polk's precise intentions were, for the Centralists in Mexico the annexation of Texas had been sufficient cause for war; they saw no disputed boundary--Mexico owned all of Texas. Before Taylor had moved to the Rio Grande, Parades had begun mobilizing troops and had reiterated his intention of attacking. On April 4 the new dictator of Mexico ordered the attack on Taylor. When his commander at Matamoros delayed, Parades replaced him, issued a declaration of war (April 23), and reordered the attack.


On Apr. 25, 1846, Mexican troops crossed the Rio Grande and ambushed a detachment of American dragoons commanded by Capt. Seth B. Thornton. Taylor's report of this ambush reached President Polk on the evening of May 9, a Saturday. On Monday, May 11, Polk presented his war message to Congress, and on Wednesday, May 13, over the vigorous opposition of the abolitionists, the U.S. Congress voted to declare war on Mexico. In the meantime two more Mexican attacks had been made across the Rio Grande at Palo Alto (May 8) and Resaca de la Palma (May 9), and both had been repulsed.

Mexican Expectations

Mexican leaders clearly expected to win these battles as well as to recover Texas and win the war. Parades spoke grandly of occupying New Orleans and Mobile. His army of about 32,000 men was four to six times the size of the original U.S. army. Furthermore, Mexican troops were well armed, disciplined, and, above all, experienced in scores of revolutions. Parades also counted on logistics. The principal theater of war would be Texas, hundreds of miles from the populous areas of the United States. Many Centralists believed that abolitionists' objections to the war would demoralize the United States, and some Centralists believed a Mexican invasion would be supported by a massive slave uprising.

Thus, the quick defeats at Palo Alto and Resaca de la Palma surprised and shocked the Mexican leadership. The U.S. victories against a larger, better trained force were attributed to the unexpected effectiveness of the American light artillery. Parades found it expedient, however, to lay the blame on his commanding general, and he quickly replaced him. The Mexican garrison evacuated Matamoros, moving to the south.

Taylor's Delay

Taylor occupied Matamoros on May 18 but then delayed for several months before moving south. He was apparently waiting for transportation promised him by the U.S. government, though his critics branded him inept. In July he moved his base up the Rio Grande to Camargo, but it was only in August that Taylor began planning the attack on Monterrey.

By that time American strength on the Rio Grande had swollen to nearly 20,000 troops, nearly all volunteers. The principal military problem was logistical support of such a quickly expanded force. The Americans were susceptible to subtropical diseases and found it difficult to maintain sanitary conditions in the camps. Fevers, dysentery, and general debility were rampant, and the mortality rate from sickness was alarming. A determined Mexican attack in July or August would have proven disastrous to the Americans.

Mexican Rebellion

The Mexicans did not attack because the Centralist government was collapsing. Rather than uniting Mexico, the war had given the Federalist faction an opportunity to rebel. Even while Taylor had been camped on the Nueces in the fall of 1845, a few Federalist leaders had been in contact with him, promising supplies and asking for assistance in overthrowing Parades. Northern Mexico was almost a Federalist stronghold, and as Taylor moved to the Rio Grande, he received increasing support from the rebels.

The defeats of the Centralist forces at Palo Alto and Resaca de la Palma precipitated open Federalist rebellions throughout Mexico. Major outbreaks at Acapulco and Guadalajara in July were followed by the defection of the military garrison of Veracruz on August 3 and that of Mexico City on August 4. Mexico was in turmoil.

On July 28, Parades turned the government over to his vice-president and went into hiding. The Centralists' government fell completely with the resignation of the vice-president on August 6. On August 22 the Federalists solemnly restored the constitution of 1824, and Valentin Gomez Farias, who had been deposed as vice-president by the Centralists in 1834, assumed temporary control of the government as the nation's only legitimate official.

In the meantime, Santa Anna had returned to Mexico. Having promised President Polk that he would work to effect a truce, he was allowed to pass through the U.S. naval blockade and land at Veracruz on August 16. Talk of a truce was forgotten. Perhaps the only leader capable of uniting the nation, he soon received command of the Mexican army; in December he was elected president by the Mexican Congress but did not formally assume office until the following March.

Monterrey and Buena Vista

In the meantime, Taylor began his advance on Monterrey. He reached that fortified town, which had a garrison of more than 10,000 troops, on September 19 and began his attack on the morning of September 21. With about 2,000 men, Gen. William J. Worth captured the road between Monterrey and Saltillo and by noon was storming Federation Hill. Six companies of Texas Rangers charged up the hill, seized the enemy artillery, and turned the cannon on retreating Mexican forces. On the opposite side of the city a diversionary attack penetrated the town, despite much confusion. On September 22 the Americans rested, but they resumed the attack the next day. After bloody street-to-street fighting, the Mexican general Pedro de Ampudia requested and was granted a truce. On September 25 he was permitted to withdraw his forces from the city, and an 8-week armistice was agreed upon. Total Mexican casualties were estimated at 367. The Americans had 368 wounded and 120 killed.

Taylor was criticized both by the military and by President Polk for agreeing to an armistice. Taylor therefore informed Santa Anna, who had assumed command of the Mexican forces at San Luis Potosi, that the armistice would be terminated early. On November 16 he occupied Saltillo. His position was strengthened by an independent force under Gen. John E. Wood, which took Parras, to the west of Monterrey, on December 5.

In January 1847, Santa Anna moved north with about 20,000 men to dislodge Taylor. Dispatches captured by the Mexicans had revealed that most of Taylor's forces were being withdrawn to take part in Gen. Winfield Scott's proposed landing at Veracruz. Word of Santa Anna's approach reached Taylor on February 21, and although outnumbered almost three-to-one, he took up a position at the hacienda of Buena Vista, a few miles from Saltillo. The Mexican attack began on February 22, when troops led by Ampudia gained an advantage and forced the Americans to abandon important defensive positions. The next morning the main Mexican force nearly overcame the U.S. defense. However, a dramatic charge led by Col. Jefferson Davis about noon and a determined artillery advance under Capt. Braxton Bragg finally saved the day for the Americans. Their casualties numbered about 700, but the Mexican losses were about 1,800. Santa Anna withdrew that night and moved south to intercept Scott's invasionary force. No further fighting occurred in northern Mexico, but Taylor remained in command of a small force there until he returned to the United States in November 1847.


The decisive campaign of the war was Scott's advance from Veracruz to Mexico City. Scott's expedition began at a staging area at the mouth of the Rio Grande in February 1847. He assembled an army of approximately 12,000, which was transported by sea to a beach about 5 km (3 mi) south of Veracruz. Landing on March 10-11, it had surrounded the city by March 15. A combined naval and land attack began on March 22. Heavy shelling from navy guns forced the almost impregnable town to surrender on March 28.

Cerro Gordo and Puebla

Almost immediately Scott began the advance toward Mexico City. Only sporadic resistance was encountered until his army reached the village of Cerro Gordo about 80 km (50 mi) inland. There, in a narrow defile, Santa Anna prepared to turn back the Americans. The attack on Cerro Gordo was led by units under William J. Worth on April 18. The U.S. engineers, who included Robert E. Lee, George B. McClellan, Joseph E. Johnston, and P. G. T. Beauregard, found a trail that enabled the Americans to envelop and rout Santa Anna's forces. The Mexicans lost 1,000 men in casualties and another 3,000 as prisoners. The Americans had 64 killed and 353 wounded.

Pursuit was impossible, but Worth moved up the road to occupy the venerable Perote Castle on April 22. Scott and the main army had entered Jalapa on April 19. There the advance stopped for a month. Scott reported over 1,000 men bedridden in Veracruz and another 1,000 sick at Jalapa.

On May 14-15, Worth and John A. Quitman moved into Puebla, about 80 km (50 mi) closer to Mexico City. They expected heavy resistance because of Santa Anna's reported presence there. However, the town's leaders and the priests had decided to open Puebla to the Americans. Santa Anna had only about 2,000 cavalry, which the Americans easily routed. Another 1,000 Americans fell sick at Puebla, apparently from the local water supply. By July 15, with recent augmentations, Scott's forces numbered about 14,000. However, over 3,000 were sick or convalescent, and the sickness rate showed no sign of decreasing.

Contreras, Churubusco, and Chapultepec

During June and July, Santa Anna frantically prepared to defend Mexico City. On August 7, Scott began his advance from Puebla, following a route over lava beds and rough land to the south of Lake Chalco that Santa Anna had left relatively unprotected. The first heavy fighting occurred on August 19-20 at Contreras, outside Mexico City, where Mexican losses were estimated at 700 and American casualties at 60. Santa Anna fell back about 8 km (5 mi) to Churubusco, where he took up a defensive position in a fortified convent. Advancing under extremely heavy fire on August 20, Scott's men finally forced the convent's surrender, although Santa Anna and much of his command escaped. Mexican losses were estimated at more than 4,000 killed and wounded and more than 2,500 prisoners; by contrast, American losses were slightly more than 1,000.

Scott might have moved promptly into the capital. Instead he granted (August 24) the armistice of Tacubaya to permit the negotiation of a peace treaty. Santa Anna used the time to muster his forces and prepare a final defense of the city. Fighting was renewed on September 7-8 at Molino del Rey, where the Americans forced the Mexican position but lost nearly 800 soldiers. The Mexican losses totaled about 2,700. The final battle for Mexico City took place at the fortified hill of Chapultepec. American artillery bombardment on September 12 was followed the next day by an infantry assault. The citadel was heroically defended by cadets from the Mexican Military College, but they were forced to surrender before noon. American troops entered Mexico City that afternoon, and shortly after midnight Santa Anna evacuated his troops.

The war was over. In just over five months, Winfield Scott had done what many had considered impossible. The duke of Wellington wrote, "His campaign was unsurpassed in military annals." On September 16, Santa Anna resigned the Mexican presidency. Forced to resign his command also (October 7), he fled the country. The new acting president, Pedro Maria Anaya, began negotiations with the American peace commissioner Nicholas Trist (1800-74) in November. Trist had just been recalled to Washington, but he decided to negotiate without credentials.


While the crucial fighting was taking place in Mexico, various U.S. expeditions effected the conquest of Mexico's territories in the American Southwest.

Kearny in New Mexico

Immediately after the declaration of war, Brigadier General Stephen Watts Kearny, stationed at Fort Leavenworth, was ordered to occupy New Mexico and California. With an army consisting largely of Missouri volunteers and numbering fewer than 2,000 (though gloriously labeled the Army of the West), he moved down the Santa Fe Trail into New Mexico in July 1846. The Mexican governor was unable to rally any resistance, and Kearny entered Santa Fe unopposed on Aug. 18, 1846. The conquest of New Mexico had, in fact, taken place through peaceful trade and commerce in the preceding years.

Kearny established a civil government with Charles Bent, a Santa Fe trader from Missouri, as governor. He then divided his command into three groups: one, under Sterling Price, was to occupy New Mexico; a second, under Alexander William Doniphan, was ordered to capture Chihuahua; the third, under his own command, headed for California. Price faced unrest and then rebellion in New Mexico in January 1847. Bent was murdered at his home in Taos. Price fought three engagements with rebels, many of whom were Pueblo Indians, and by mid-February had the revolt under control.

Doniphan and the Missouri Volunteers struggled down the Rio Grande, suffering many privations along the route, to reach the vicinity of present El Paso, Tex., late in December 1846. On Christmas Day at El Brazito they were attacked by a small detachment of Mexicans who were easily routed. The Missourians rested at Paso del Norte (present Ciudad Juarez) until Feb. 8, 1847, when the march to Chihuahua City began. On February 28 the Americans won a decisive victory at the crossing of the Sacramento River just outside Chihuahua. Their casualties consisted of one killed and five wounded; Mexican losses were about 300 dead and another 300 wounded. In May, Doniphan took his command eastward to Saltillo to join Taylor's forces.

Kearny set out for California on September 25 with only 300 dragoons. At Socorro, N. Mex., they met the famous guide Kit Carson, who was returning from California. Learning that the conquest of California was virtually complete, Kearny sent 200 of his men back to Santa Fe and, led by Carson, continued to California.

Conquest of California

The American settlers in California had revolted against Mexican rule and established (June 1846) the Bear Flag Republic, under John C. Fremont, before news of the war reached them. On July 2, U.S. Commodore John Drake Sloat landed at Monterey. He proclaimed U.S. jurisdiction on July 7 and two days later occupied San Francisco. However, California was by no means under U.S. control. Mexican authority in California was divided between two rivals, Pio Pico in Los Angeles and Jose Castro in Monterey. Following the American landing, Castro headed south, apparently to attempt reconciliation with Pico and resistance to the United States. However, Commodore Robert Stockton, who replaced Sloat on July 23, sailed down the coast and landed troops under Fremont at San Diego and others near Los Angeles. Pico and Castro fled on August 10.

Heavy-handed martial law administration precipitated a revolt in southern California in September. Led by Jose Maria Flores, the rebels had expelled the Americans from Los Angeles and San Diego by the end of October. On Dec. 6, 1846, Kearny, en route to San Diego, met the rebels in an indecisive action at the Battle of San Pascual. Joining Stockton, who had arrived at San Diego, Kearny defeated a rebel band near Los Angeles on the San Gabriel River on Jan. 8-9, 1847. On January 13, Fremont received the final surrender of the rebels and signed the Treaty of Cahuenga. At the end of the month another American expedition, "half naked and half fed," reached San Diego. The remnant of 500 Mormon volunteers under Phillip St. George Cooke, it had marched from Utah to Sante Fe and across scorching deserts in southern New Mexico and Arizona.

After a bitter dispute among Stockton, Fremont, and Kearny, the last established a provisional government in California. With California secure, the U.S. Navy attempted the conquest of Mexican ports on the Pacific, capturing Mazatlan (Nov. 11, 1847), Guaymas (Nov. 17, 1847), and San Blas (Jan. 12, 1848).


Despite the objections of the abolitionists, the war received enthusiastic support in all sections of the United States and was fought almost entirely by volunteers. The army swelled from just over 6,000 to over 115,000. Of this total approximately 1.5 percent were killed in the fighting, and nearly 10 percent died of disease; another 12 percent were wounded or discharged because of disease or both. For years afterward, Mexican War veterans continued to suffer from the debilitating diseases contracted during the campaigns. The casualty rate was thus easily over 25 percent for the 17 months of the war; the total casualties may have reached 35-40 percent if later injury- and disease-related deaths are added. In this respect the war was the most disastrous in American military history.

During the war political quarrels arose regarding the disposition of conquered Mexico. A strong "All-Mexico" movement urged annexation of the entire territory. Abolitionists opposed that position and fought for the exclusion of slavery from any territory absorbed by the United States. In 1847 the House of Representatives passed the Wilmot Proviso, stipulating that none of the territory acquired should be open to slavery. The Senate avoided the issue, and a late attempt to add it to the Treaty of Guadalupe Hidalgo was defeated.

The Treaty of Guadalupe Hidalgo was the unsatisfactory result of Nicholas Trist's unauthorized negotiations. It was reluctantly approved by the U.S. Senate on Mar. 10, 1848, and ratified by the Mexican Congress on May 25. Mexico's cession of California and New Mexico and its recognition of U.S. sovereignty over all Texas north of the Rio Grande formalized the addition of 3.1 million sq km (1.2 million sq mi) of territory to the United States. In return the United States agreed to pay $15 million and assumed the claims of its citizens against Mexico. A final territorial adjustment between Mexico and the United States was made by the Gadsden Purchase in 1853.


Bauer, K. Jack, The Mexican War (1974); Bill, Alfred H., Rehearsal for Conflict: The War with Mexico, 1846-1848 (1945; repr. 1970); Connor, Seymour V., and Faulk, Odie B., North America Divided: The Mexican War, 1846-1848 (1971); Dufour, Charles L., The Mexican War: A Compact History (1968); Eisenhower, John S. D., So Far from God: The U. S. War with Mexico, 1846-48 (1989; repr. 1990); Johannsen, R. W., To the Halls of the Montezumas: The Mexican War in the American Imagination (1985; repr. 1988); Nichols, Edward J., Zach Taylor's Little Army (1963); Ruiz, Ramon E., ed., Mexican War (1963); Schroeder, J. H., Mr. Polk's War (1974); Singletary, Otis A., Mexican War (1960); Smith, Justin H., War with Mexico, 2 vols. (1919; repr. 1963); Weems, J. E., To Conquer a Peace (1988)

For more information, look at the Descendants of Mexican War Veterans site.


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