10 Events of the Mexican-American War

10 Events of the Mexican-American War

Larry Holzwarth - July 22, 2018

The Mexican – American War, known in the United States as simply the Mexican War, was a conflict in American history which Ulysses Grant referred to in his memoirs as, “…one of the most unjust ever waged by a stronger against a weaker nation. It was an instance of a republic following the bad example of European monarchies, in not considering justice in their desire to acquire additional territory.” Grant was a veteran of the war, acquitting himself well in combat, and many of the officers of both sides of America’s Civil War received their baptism under fire while facing Mexican guns.

It was a war of simple conquest, with the United States acquiring the lands which became California, Arizona, Nevada, New Mexico, Utah, and Colorado. It was a war which the United States provoked and prosecuted with determination, using a mostly volunteer Army by professional officers for the most part trained at the United States Military Academy. It was controversial before and after it was fought, and its aftermath heightened the debate over slavery in the conquered lands, where it had been abolished by the Mexican government. Under Mexico, the native tribes of the southwest were considered citizens, a right denied them by the United States. It was the capping triumph of manifest destiny.

10 Events of the Mexican-American War
The Administration of President James Knox Polk provoked the war with Mexico as a means of acquiring California. Wikimedia

Here are ten events of the Mexican War which made the United States a continental power, stretching from sea to shining sea.

10 Events of the Mexican-American War
Texas won its independence from Mexico at the Battle of San Jacinto in 1836. Mexico refused to recognize the Republic of Texas. Wikimedia


When Texas was a Mexican state, its sparse population was subject to the depredations of the Cheyenne, which controlled a vast portion of the territory. Mexico opened the region to settlement by migrants coming from America, and motivated by the potential to create large estates Americans poured into the region. Disputes with the Mexican government led to Texas declaring itself independent in 1836, and the Texas Revolution, including the legendary Battle of the Alamo, established independence as fact. The United States recognized the Republic of Texas, though Mexico did not, and the border between Texas and Mexico remained in dispute.

In 1845 President James K. Polk, a fervent believer in Manifest Destiny, offered to annex Texas as the 28th American state. Texas entered the Union in December as a slave state, over the diplomatic protests of the Mexican government. Polk then offered to resolve the disputed border by purchasing the region between the Nueces River – which Mexico claimed was its northern border – and the Rio Grande, which was claimed by Texas to be its southern border. Mexico declined the offer. Polk responded by moving American troops into the disputed region, placing American outposts along the Rio Grande, in what the Mexicans claimed was their territory.

Polk’s motivation was not protecting Texas. He was aware of potential British Territorial ambitions in Upper California, and wanted the region for the United States. Following its independence from Spain, Mexico had withdrawn most of its military presence from Upper California (the region north of the Baja Peninsula) and the sparse settlements there were neglected by the Mexican government. President Tyler’s administration had suggested acquiring California by purchasing the port of San Francisco, but the Mexican government declined. The Polk administration was determined to stretch American territory to the west coast.

The troops Polk stationed in the Mexican territory established fortifications, an indication that their presence on Mexican land was intended to be permanent. At the same time an American expedition in California under John C. Fremont built fortifications in California. The Mexican government was in a state of disruption, and some Mexican leaders called for war with the Americans, while others argued forcefully against military action. By late 1846 the Mexican government was controlled by nationalistic factions, and American diplomat John Slidell, who had been attempting to negotiate the purchase of California and Nueva Mexico (the land between Texas and California) returned to the United States.

When the Mexican government demanded the US withdraw its troops to an area north of the Nueces River, American commander Zachary Taylor refused, and instead erected more fortifications along the Rio Grande. According to Ulysses S. Grant, a lieutenant with the American troops, “…we were sent to provoke a fight, but it was essential that Mexico should commence it.” In the spring of 1846, Mexican troops attacked an American patrol under the command of Captain Seth Thornton, which became known as the Thornton Affair. The following month, May of 1846, Mexican troops besieged Taylor’s garrison at Fort Texas.

10 Events of the Mexican-American War
General Zachary Taylor, veteran of the War of 1812, in a daguerreotype from about 1845. Wikimedia

The Early Battles in Texas.

When Fort Texas was besieged, Zachary Taylor led a force to relieve the garrison. This force was engaged by a larger Mexican force at the Battle of Palo Alto. The superiority of the American artillery drove the Mexicans back, and they established fortified defenses at Resaca de la Palma. During the battle there the following day the Mexican army was again forced to retreat, after fierce combat, and the retreat became a rout, with the fleeing Mexicans struck repeatedly by pursuing American cavalry. The Mexicans were driven across the Rio Grande by American troops, which paused once they reached the river.

On May 11, 1846, President Polk sent a war message to Congress, citing the Mexican actions in the disputed region known as the Nueces strip as acts of war. Congress approved the declaration of war on May 13. One congressman who disputed the President’s statement, which accused Mexico of attacking American troops on American soil, was Abraham Lincoln. Lincoln argued that the attacks occurred against American troops which were on Mexican soil, or at any rate on disputed territory which had formerly been claimed by Spain and later by Mexico. Most American abolitionists opposed the war, believing it was an attempt to increase territories which would allow slavery.

Henry David Thoreau vocally opposed the war and refused to pay taxes which would be used to support the American war effort, an act for which he was jailed. In response Thoreau wrote the essay Civil Disobedience, which was published in 1849, after the war was over. In the essay Thoreau argued against the actions of the government and posited that it was the duty of citizens to rise in opposition to governments which acted without conscience. Throughout Thoreau’s New England, the vocal majority opposed the war and the actions of the government under Polk, spurred by abolitionists who believed the war was about spreading slavery.

Their arguments were soon drowned out by the patriotic celebrations which erupted with the news of Zachary Taylor’s military victories over the Mexicans at Palo Alto and the retreat of the Mexicans across the Rio Grande. Newspapers dispatched journalists to the Mexican border, where they joined the American troops and sent back jingoistic stories of American morale and military superiority. The War Department developed a plan to invade Mexico in the west using troops from Fort Leavenworth and the Jefferson Barracks in Missouri, as well as a simultaneous invasion by the troops under Zachary Taylor. A US Naval squadron was sent to the Pacific to support the western invasion.

In Mexico, the defeat of the Mexican troops at Palo Alto and Resaca de la Palma led to the resurgence in power of military hero Antonio Lopez de Santa Anna, who returned from Cuban exile, renounced any political ambitions, and offered his services as a military commander. Santa Anna was encouraged to return to Mexico by US agents sent by President Polk, who offered the former dictator a bribe of $2 million to be paid upon Mexican cession of California. Once Santa Anna reached Mexico City, after being allowed to pass through the American blockade, he reneged on all of his promises and took command of the Mexican Army, declared himself president, and began operations against the American invasion.

10 Events of the Mexican-American War
John C. Fremont’s conquest of California achieved Polk’s main war aims before the worst of the fighting even began. Wikimedia

The invasion of western Mexico

An American army from Fort Leavenworth, commanded by Stephen Kearny, occupied Santa Fe in August 1846, declared New Mexico a territory of the United States, and established a provisional government, without a shot being fired. Kearny proclaimed himself its military governor. The army then moved west to California, leaving behind a garrison under Sterling Price, with Charles Bent as governor of New Mexico. In January, 1847, an insurgency arose against the Americans which severely wounded Bent, including scalping him in his home in the presence of his family. A series of battles between the American garrison and the insurgents quashed the rebellion.

American settlers in California rebelled against the weak Mexican government there, and ships of the US Navy seized Yerba Buena Bay (now San Francisco) supporting the settlers and American troops under John Fremont. Meanwhile Kearny’s army marched overland to Southern California. Bloody fighting took place between Kearny’s troops and Mexican forces, but the Mexicans were steadily pushed back, and by winter the American’s occupied Los Angeles and most of the other settlements in California. In January Mexican commanders agreed to surrender, and in the Treaty of Cahuenga ceded all of California north of the Baja Peninsula to the United States.

In the spring of 1847 the United States Pacific Squadron destroyed the Spanish shipping in Baja California, and troops and Marines raided its major ports and facilities. Mexican forces undertook campaigns to reclaim the ports, and a series of battles occurred throughout 1847, but the Americans retained the ports until evacuating them following the cessation of hostilities. In Baja California, the United States had support of Mexican citizens unhappy with the national government since Spain was ousted, and many of those citizens accompanied the Americans when Baja California was evacuated at the end of the war.

The seizure of what was then known as Upper California (Alta California) was the true goal of the Polk Administration in its pursuit of war with Mexico. The region known as Nueva Mexico, between the state of Texas and the Sierras, was of little concern other than it provided a contiguous link to the west coast settlements. California, with its fertile valleys and fine harbors, was desirous both to curtail European settlement on the continent through the expansion of Canada and Mexico, and to provide the United States with unimpeded access to the Pacific. Baja California was less desirable, and in the treaty which ended the war was returned to Mexico, despite American occupation.

Shortly after the end of the war gold was discovered in California, and the sparsely settled region was inundated with those hoping to strike it rich. California’s population exploded. The region, rich with Spanish names and traditions, became home to great ports and the former settlement of Yerba Buena grew quickly into the city of San Francisco. The seizure of California and Nueva Mexico diminished the acreage of Mexico by nearly half, and ensured that the United States would occupy the North American continent from the Canadian border to as far south as it demanded in treaty negotiations with the Mexicans.

10 Events of the Mexican-American War
Antonio Lopez de Santa Anna agreed to transfer California to the United States if allowed to return to Mexico from exile in Cuba, in exchange for $2 million. He later reneged. Wikimedia

The invasion of Northeastern Mexico

After Zachary Taylor’s defeat of the Mexican troops north of the Rio Grande he led his army into Mexico and laid siege to the city of Monterrey. Monterrey was fortified with many battlements built of stone, and the American artillery, which had been effective against the Mexican troops at Palo Alto and Resaca, was unable to reduce them. For the first time, American infantry was forced to engage in urban warfare, fighting house to house in an attempt to capture the city. The infantry was forced to engage houses one at a time, either entering through windows or using demolitions to batter down the walls in order to engage their enemy in fighting which was often hand to hand.

Casualties were heavy among the American troops, but gradually Mexican forces were driven back. They prepared a final stand in the city near its public buildings in the town’s main square, where American artillery could reach them in the open. The Mexicans surrendered on September 24, and Taylor allowed the remaining Mexican troops to withdraw, granting an armistice of eight weeks during which the Mexicans agreed to cease hostile actions against American positions. Taylor needed the respite to rest his own exhausted forces. The American army had cleared the larger Mexican army from a well-fortified position and captured a significant prize.

Despite Taylor’s clear victory, Polk was furious when he was informed of the armistice. He was also concerned over the rise in Taylor’s popularity following his third major defeat of the enemy. Polk announced that Taylor had no authority to grant an armistice or any other form of cease fire, and ordered his general to advance against the enemy. At the same time the opposition press in the United States reported atrocities committed by the American troops in Monterrey and neighboring towns and hamlets, which Taylor did not bother to deny. Instead the reported rapes and murders of civilians were blamed on volunteer troops, rather than the American regulars.

With Polk demanding action, Taylor violated the armistice and moved units of his army further south, seizing Saltillo, and creating a fortified position in the mountains at Buena Vista. Santa Anna moved north to attack him, at the head of an army of 20,000 men. Taylor had less than five thousand troops. The Mexican Army endured significant numbers of deserters as it moved to the north, by the time it reached Taylor’s lines it had lost nearly 5,000 men. Still, it outnumbered the Americans by a factor of three to one, and Santa Anna, with the flamboyance for which he was known, demanded that the Americans surrender.

The ensuing Battle of Buena Vista was a victory of superior American firepower, from both artillery and infantry. The Mexican assaults were repulsed despite their overwhelming numbers, and the American line held throughout the afternoon of February 22, 1847. The battle was fought in a narrow mountain pass, which limited the ability of the Mexican army to maneuver into advantageous positions. The following day the American lines again held against repeated Mexican assaults. When Santa Anna broke off the attacks and withdrew, Taylor did not pursue the still larger Mexican force. It was yet another victory for Zachary Taylor, and he was celebrated in the United States as America’s foremost soldier.

10 Events of the Mexican-American War
Winfield Scott’s army being landed below Veracruz, the beginning of the campaign to take Mexico City. WIkimedia

Naval operations against Tabasco

In the spring of 1846 the United States Navy established a blockade against the east coast of Mexico, shutting down the ports and preventing supplies and trade goods from reaching the country. In the fall of the same year, the US Navy began aggressive actions against Mexican bastions along the Tabasco River, using a squadron of steamers and sailing schooners under the command of Matthew Calbraith Perry, whose brother, Oliver Hazard Perry, had been one of the naval heroes of the War of 1812. Perry’s squadron twice assaulted the towns of San Juan Bautista and Frontera, using heavy naval bombardments and landing parties.

After Perry captured the ports along the Tabasco (today’s Grijalva River) Mexico was sealed off from the outside world by sea. The Mexican state of Tabasco, as well as the state of Chiapas, rose in revolt against the Mexican government, seeking to join the nation of Guatemala. Emissaries from the insurgents sought out Perry to ask for his support. Perry declined, continuing to patrol the river and denying supplies to the Mexicans. The American troops dispatched to garrison San Juan Bautista and other towns along the river were soon stricken with yellow fever, and brought under frequent attacks by guerrillas and bandits.

Following Taylor’s victory at Buena Vista President Polk ordered his army to remain in place, and transferred a significant number of his troops to the command of Major General Winfield Scott. Scott’s army was to be used for the main thrust into Mexico, supported by naval forces which attacked at Veracruz. The fortifications around Veracruz were considered the most formidable in the world other than Gibraltar, and were well manned. The Americans planned to land troops south of the fortifications, which were bombarded by naval ships, after which they would be encircled by the American troops and the city reduced by siege.

The United States Army and Navy had not engaged in a major operation of such a nature before. The Navy was responsible for placing the army with its artillery, horses, supplies, and troops of cavalry and infantry ashore, in a manner which allowed it to immediately enter combat. Ships of lesser draft were positioned closer inshore to provide covering artillery fire as the army disembarked. Larger ships provided covering fire over the heads of the small boats oared by navy crews as they crawled to the beach. The Mexican Army was taken by surprise and the entire American army of 8,600 men was landed without casualties.

The landing at Veracruz was the first amphibious assault undertaken by the United States Army in its history, and one of the most successful. By the evening of March 9, 1847, the American army was entirely in position for an assault on the port of Veracruz, which when taken would open the road to Mexico City. The US Navy then supported the military operation against the fortifications through the construction of a naval battery ashore, using the heavy guns from the supporting ships. The battery was constructed by a young member of the Army Corps of Engineers, Captain Robert E. Lee, in a position from which it could readily destroy the enemy’s works.

10 Events of the Mexican-American War
A Nathaniel Currier lithograph of the American bombardment of Veracruz, published in 1847. Library of Congress

The invasion of central Mexico

Once the American army was ashore below Veracruz it moved quickly to surround the city and its defenses, establishing siege lines by St. Patrick’s Day, 1847. The Mexican fortifications included Fort Santiago, located to the south of the city and Fort Concepcion to the north of the city, on an elevated position. Fort San Juan de Ulua was constructed on a reef offshore from the town, and was not directly attacked by the Americans, other than by long range bombardment from naval ships. As the Americans moved into position they repelled sorties from the Mexican garrisons, and placed troops further inshore to prevent Mexican reinforcements from reaching Veracruz.

On March 22 the American artillery began a systematic bombardment of the town and fortifications, supported by naval gunfire. The walls of the fortification were largely built of coral, mined from the reef outside the harbor, and the heavy naval guns made short work of them. US troops and ships fired rockets over the walls of the fortifications, which did relatively little damage, but were effective in creating a sense of terror among both civilians and the besieged troops. On March 24 a relieving force of 2,000 Mexican troops were encountered by American troops and driven back in sharp fighting. With no possibility of relief the Mexican commander, Juan Morales, requested a parley.

Morales asked for a cease-fire to allow the evacuation of civilian women and children from the city on March 25. American commander Winfield Scott refused and again demanded the city surrender. On the evening of March 25 Morales resigned his command rather than acceding to the recommendation of his officers that he surrender the post. He was replaced by General Jose Landero. On the morning of March 26 Landero requested terms from Scott. Veracruz and its fortifications, including San Juan de Ulua, were handed over to the Americans on March 28, and Scott established garrisons for the city before setting out on the road to Mexico City.

Scott began moving the American army inland on April 2, sure that the city and port were safe from attack. At the same time, Mexican General Santa Anna was moving east. Scott’s army consisted of about 8,500 men, while Santa Anna commanded just over 12,000. Santa Anna positioned his army in a fortified mountain pass near Xalapa, northwest of the city of Veracruz, which was known as Cerro Gordo. The leading elements of Scott’s army arrived on April 12, and engineers scouted the position for the best placement of American artillery. One of the engineers, Lieutenant Pierre Gustavus Beauregard, observed that the taking of neighboring Atalaya Hill would make the Mexican position untenable.

In order to take the hill roads were necessary to enable the placement of artillery. The Army Corps of Engineers officers, under the supervision of Captain Robert E. Lee, created a road up the steep slopes of the hill under the cover of darkness, and artillery was moved into possession by manpower alone, since the slopes were too sleep for mules and horses. One by one the guns were moved into position to cover an infantry assault on Atalaya Hill, which was taken on April 17. The assault allowed American troops to effectively surround the Mexican Army, attacking it from the rear. By ten in the morning of April 18, most of the remaining Mexican troops had either fled or surrendered.

10 Events of the Mexican-American War
US troops at the Battle of Cerro Gordo in 1847, yet another significant victory for the American Army. Wikimedia

Advance upon Mexico City

Santa Anna fled the Battle of Cerro Gordo in such a hurry that he left behind his artificial leg. The severe defeats the Mexican general had suffered severely undermined Mexican morale and civilian support for the war against the Americans. When Scott’s army approached the Mexican city of Puebla it surrendered without defense on the first of May. Scott paused at Puebla to rest his troops and replenish supplies for a push forward to Mexico City, as well as strengthen his lines of supply to Veracruz. Scott sent troops forward to reconnoiter, and patrolled the areas around Puebla against guerrilla bands, before moving forward again in August.

In all, Santa Anna had just less than 30,000 men in position to defend Mexico City, but they were spread over a wide area, and many were inexperienced troops. Scott’s army first made contact with the Mexicans on August 19 near Contreras. An American party building a road on which they could attack the Mexican town of San Antonio were attacked by elements of the Mexican Army, and both sides rushed reinforcements to the scene. The fighting raged until dark. During the night American patrols discovered a path which could be used to get around the Mexican troops and attack them from the rear. Their assault the following morning drove the Mexicans from the battlefield in fewer than twenty minutes.

The Mexican defenses reformed near Churubusco and on August 20 they were attacked by units of Scott’s army. Mexican troops occupied a convent and entrenched along its front. The fighting throughout the afternoon was ferocious, and the Mexicans gradually were reduced to those occupying the convent. Within the building were members of the unit known as the St. Patrick’s Battalion (San Patricios) who refused to allow the other units within the surrounded building to surrender, on at least three occasions pulling down white flags held aloft by men of other units. The battle continued until the Americans were ordered to halt.

The San Patricios did not continue the fight out of an excess of courage. The battalion was comprised mostly of American immigrants from Catholic countries, who had deserted the American Army, preferring to fight for Catholic Mexico. They feared that if they surrendered to the Americans they would be dealt with harshly, at the very least whipped for desertion, and possibly executed for treason. The battle for Churubusco led to the Americans taking over 1,600 prisoners, including three Mexican generals. The United States Army was in position to take Mexico City following the victory, though the fighting was not yet over.

The victory at Churubusco led to the opening of talks regarding an armistice, which continued until September 6. Despite the presence of the American Army outside of their capital city the Mexican commissioners were unwilling to concede the gains made by American troops and Scott, who had deliberately left Mexico City unscathed, was forced by Mexican intransigence to renew the assault on September 8. Santa Anna had used the armistice to prepare for additional fighting around the city. On September 8, 1847 the Americans and Mexican fought yet another bloody battle at Molino del Rey, on the outskirts of Mexico City.

10 Events of the Mexican-American War
The storming of Chapultepec led to an assault on Mexico City’s gates, and the ultimate collapse of Mexican resistance. Wikimedia

The Capture of Mexico City

Molino del Rey (King’s Mill) was a group of low stone buildings less than a mile from the Castle of Chapultepec, which was located two miles from Mexico City’s gates. The buildings were reported to Scott as being used for the casting of cannon, ordered by Santa Anna as the peace talks were ongoing. The Americans attacked the position on September 8, and in heavy fighting, which included subduing the stone buildings one by one, destroyed the Mexican position. The attacking Americans came under fire from artillery within the castle during the assault, and casualties were heavy. After destroying the Molino del Rey the Americans still had to clear Chapultepec.

Chapultepec stood on the summit of a 200 foot hill outside the western gates of Mexico City. In 1847 it housed the Military Academy of Mexico, and was defended by just under 900 men, both within its walls and in external fortified defensive positions which covered its approaches. On September 12 Scott’s artillery bombarded the castle throughout the day, suspending the cannon fire during the night. On the following morning the artillery attack resumed. At 8 AM the Americans assaulted the castle and fortifications in three columns. The assault lasted just over an hour before the castle fell into American hands.

During the assault five Mexican cadets refused to withdraw when ordered by the garrison commander and remained to fight to the death. They were between the ages of 13 and 19, and remained by the side of one of their instructors. They are honored as the Los Ninos Heroes in Mexican culture, and a monument to their memory stands on the grounds of the castle Mexico City. The American attack did not stop with the capture of the castle, troops were quickly reformed and supporting units brought forward for the assault on Mexico City. By early evening American troops were through the gates of Mexico City, though Mexican troops remained in its major fortification, the Ciudadela.

The following morning, shortly after midnight, Santa Anna ordered a withdrawal of the remaining Mexican troops, to Guadalupe Hidalgo. Later that morning the civilian authorities of Mexico City surrendered to General Scott. Mexican resistance was not yet over, though Scott declared himself governor of the captured Mexican territory, and dispatched some of his troops to secure his lines of communication with Veracruz. He also reinforced the garrison at Puebla when Santa Anna launched an attack against the city late in September. Santa Anna was defeated at the Battle of Huamantla in October, ending his military career.

Throughout the fall of 1847 American troops continued to suppress guerrilla raids, which were often as much bandits plundering the defenseless Mexican villages as they were fighters against the American invasion. As they did Nicholas Trist represented the Americans at the treaty negotiations in Guadalupe Hidalgo, where he ignored President Polk’s instructions to include Baja California in the land to be ceded by Mexico to the United States, leading him to be fired after the Mexicans and Americans had signed the treaty. Faced with the smaller acquisition, which still was still more than half of the Mexican territory before the Texas Revolution, Polk had no choice but to accept the treaty.

10 Events of the Mexican-American War
American deserters and other foreign volunteers served in the Mexican army in the San Patricios, present in several engagements. Wikimedia

The San Patricios

The Saint Patrick Battalion was formed of mostly American immigrants from Ireland by John Riley, who deserted from the British Army in Canada, fled to the United States, joined the US Army, and when war with Mexico broke out, deserted the American Army as well. In April 1846 he deserted to the Mexicans at Matamoros. He formed the battalion from fellow Irish deserters as well as those from Germany, Scotland, the Italian peninsula, and many other countries who had been in the United States Army when the war with Mexico broke out. The battalion was formed as an artillery unit, and engaged the Americans in several battles.

Desertion was a problem for both armies during the war with Mexico, though less so for the Americans than the Mexicans. The American desertion rate was just over 8%; that of the Mexicans was well over 20%. The Mexican government promised substantial rewards for American deserters coming over to their side, including land and gold, which never materialized. Instead many of the deserters found themselves taken prisoners by American troops following defeats in battle. They were enticed with religious arguments as well, with the Mexican propaganda insisting that the war was as much against their shared faith of Roman Catholicism as it was against the Mexican government.

In 1847 Santa Anna ordered the San Patricios reorganized as an infantry unit and placed under the command of a Mexican officer. Volunteers from other European countries were added to its ranks. The San Patricios fought in the battles against Winfield Scott’s army as it pounded its way into Mexico City. The San Patricios were finally defeated at the battle of Churubusco. Of the deserters who surrendered to the American troops, those determined to have left the American army following the outbreak of the war were tried for treason and executed. Forty-eight were executed by hanging, one by firing squad. Thirty were hanged at Chapultepec as the castle was taken.

In Mexico the American deserters were received as heroes, a status they have retained over the years. In the United States the army refused to admit the existence of the San Patricios as a formal unit in order to discourage further desertion from the army of occupation in Mexico. Not until 1915 did the US Army formally admit that it had covered up the existence of the battalion. By then it had become known in Mexican and American folklore, particularly among those of Irish descent. During the 1852 presidential election Winfield Scott campaigned for president, and his treatment of the battalion became an issue with Irish voters.

The motives for the San Patricios who deserted the United States Army to serve in the Mexican Army, where the pay was less, the food worse, and the leadership poor, were as varied as the men themselves. Most army deserters simply tried to go home, not wanting to serve in any army. The San Patricios instead fought well with the Mexican army until the closing days of the war. Most who survived remained in Mexico following the war, though some returned to their homelands. They were not welcome in the United States and few attempted to return there. Many lived the rest of their lives begging on the streets of Mexican towns and villages.

10 Events of the Mexican-American War
American heavy cavalry charge the Mexican lines at the Battle of Resaca de la Palma in Texas in 1846. US Army

The impact of the Mexican War

The Mexican War enhanced the prestige of the United States Military Academy at West Point, and many of its graduates became household names. The Army Corps of Engineers and its officers, in particular Robert E. Lee, were esteemed for their professionalism under fire. Several political careers were launched by veterans, including by Franklin Pierce, who defeated his fellow veteran Winfield Scott for the presidency in 1852. Zachary Taylor was elected president in 1848, as Polk had feared when the general developed his reputation early in the war, but Polk did not run for re-election against him, having previously pledged to serve only one term.

The Mexican War was the first experience of combat for many of the officers who later served in the American Civil War, on both sides of the conflict. The leadership of the young junior officers and their observations of how their men behaved under fire, and among the civilian population of occupied territories, did much to inform their treatment of their men in the later conflict. They also established the tactics which would later be used in the Civil War, many of which by then had become outdated by the improvements in weapons. The coordinated operations between the army and navy were repeated in the Civil War along the rivers and inlets of the American coast.

The Mexican War led to regional debates in Congress, over slavery in the new states and territories from the lands acquired, for which Mexico was compensated in the Treaty of Guadalupe Hidalgo. Mexico was given $15 million in compensation for the loss of land and the United States assumed responsibility for debts of the Mexican government to settlers in the new American territories of $3.25 million dollars. The vast land acquisition became known as the Mexican Cession as a result of the compensation, rather than the conquest which it was. The amount paid was less than half of what Polk had been willing to pay for the land before the war.

Within one year of the end of the war, gold was discovered in California, followed by the silver strikes in Nevada. Within a decade the Pony Express was connecting California with the east, and plans were underway for a transcontinental railroad, which were disrupted by the Civil War. In 1848 the town of San Francisco had about 1,000 inhabitants. At the end of the following year it held more than 25,000. Other areas within the land of the Mexican Cession grew far more slowly, occupied by the Native American tribes hostile to American settlement.

As America became more divided over the issue of slavery many pointed to the Mexican War as the point of no return. When former president Grant wrote his memoirs, which included his service in the Mexican War, he wrote, “The Southern rebellion was largely the outgrowth of the Mexican war.” Unlike Robert E. Lee, Grant left the army for a time, returning as a volunteer when the Civil War broke out. So did several other officers, as competition for posts became stiffer in the peacetime army. What posts existed were largely isolated outposts among the Indians, and military careers featured slow advancement. Even Robert E. Lee was still a Colonel when the Civil War erupted, more than a decade following the Mexican War.


Where do we find this stuff? Here are our sources:

“Personal Memoirs of U.S. Grant”, by Ulysses S. Grant, 1885

“Lessons of the Mexican War”, by Norman A. Graebner, Pacific Historical Review, 1978, online

“Fremont Steals California”, by Sally Denton, American Heritage Magazine, Winter, 2011

“The US and Mexico at War”, by Donald S. Frazier, 1998

“So Far From God: The U. S. War with Mexico, by John Eisenhower, 1989

“Surfboats and Horse Marines: U. S. Naval Operations in the Mexican War, 1846-48”, by K. Jack Bauer, 1969

“Santa Anna of Mexico”, by Will Fowler, 2007

“Brainpower and Brawn in the Mexican – American War”, by William Rosen, Smithsonian Magazine, July 16, 2013

“The San Patricios”, by James Callaghan, American Heritage Magazine, November 1995

“A Nice Piece of Real Estate”, by Richard Reinhardt, American Heritage Magazine, December 1971