Mexican-American War

The Mexican–American War, also known in the United States as the Mexican War, and 
in Mexico as la invasión estadounidense (the United States Invasion), la intervención 
norteamericana (the North American Intervention), or la guerra del 47 (the War of '47) was 
a military conflict fought between the United States and Mexico from 1846 to 1848, in the 
wake of the 1845 U.S. annexation of Texas. Mexico had not recognized the secession of 
Texas in 1836 and announced its intention to take back what it considered a rebel province.

In the United States, the war was a partisan issue, supported by most Democrats and 
opposed by most Whigs, with popular belief in the Manifest Destiny of the United States
ultimately translating into public support for the war. In Mexico, the war was considered a 
matter of national pride.

The most important consequence of the war was the Mexican Cession, in which the 
Mexican territories of Alta California and Santa Fé de Nuevo México,were ceded to the 
United States under the terms of the Treaty of Guadalupe Hidalgo. In Mexico, the enormous 
loss (52%) of territory encouraged the central government to enact policies to colonize its 
northern territories as a hedge against further losses.

After Mexico gained independence from the Spanish Empire at the end of the Mexican 
War of Independence in 1821, The Mexican Empire inherited ownership of the provinces 
of Alta California, Nuevo Mexico, and Texas, from Spain. (These territories are now 
States within the United States of America.) Weakened and virtually bankrupt from the 
Mexican War of Independence, the new Mexican government found it difficult to govern 
its northern territories, which in any case were as far as two thousand miles from the 
capital, Mexico City.

The First Mexican Empire ruled by Agustín I of Mexico (Iturbide) opposed the American 
idea of selling Texas because it was trying to colonize the northern part of the Mexican 
Empire. After the fall of the Emperor Agustin in 1823, the government of Mexico maintained 
the position of not selling Texas.

In 1836, General Antonio López de Santa Anna, abolished the 1824 federal constitution and 
established a new constitution that attempted to centralize power. The new centralist 
constitution enshrined the Siete Leyes which included secular reforms but granted additional 
powers to the president such as the power to close congress and suppress the judiciary. 
Several Mexican states rebelled against the new central government under Santa Anna, 
including Texas (then a department of the state of Coahuila y Tejas), San Luis Potosí, 
Querétaro, Durango, Guanajuato, Michoacán, Yucatán, Jalisco and Zacatecas.

Many Texans were slave owners and objected to the abolition of slavery. A violent insurgency, 
known as the Texas Revolution, started in 1836. General Santa Anna responded by 
engaging in two battles against rebel forces, the Álamo and Goliad, which encouraged a 
wider revolt in Texas.

In the successful 1836 Texas Revolution, Texas won its independence after defeating Santa 
Anna and the Mexican army. General Santa Anna was taken captive by the Texans militia 
and released only after signing the Treaties of Velasco in which he promised to recognize 
the sovereignty of the Republic of Texas. When he returned to Mexico City the government 
refused to recognize the loss or independence of the Republic of Texas because, it said, 
Santa Anna was not a representative of Mexico and that he signed away Texas under 
duress. Mexico declared its intention to recapture what it considered a breakaway state.

In the decade after 1836, Texas consolidated its position as an independent republic by 
establishing diplomatic ties with Britain, France, and the United States. Most Texans 
were in favor of annexation by the United States, but U.S. President Andrew Jackson 
rejected it.

Under U.S. President James K. Polk, Texas was admitted to the union in 1845, when it 
became the 28th state. The Mexican government had long warned that annexation meant 
war with the United States. Britain and France, which recognized the independence of 
Texas, repeatedly tried to dissuade Mexico from declaring war against a much more 
powerful neighbor. British efforts to mediate were fruitless in part because additional 
political disputes (particularly the Oregon boundary dispute) arose between Britain and 
the United States.

In 1845 U.S. President James K. Polk sent diplomat John Slidell to Mexico City in an 
attempt to purchase Mexico's California and New Mexico territories. U.S. expansionists 
wanted California as a way to thwart British ambitions in the area and to have a Pacific 
Ocean port. Polk authorized Slidell to forgive the $4.5 million owed to U.S. citizens from 
the Mexican War of Independence and pay another $25 to $30 million in exchange for the 
two territories.

However, Mexico was not inclined nor in a position to negotiate. In 1846 alone, the 
presidency changed hands four times, the war ministry six times, and the finance ministry 
sixteen times. Mexican public opinion and Mexican political factions and leaders felt 
Mexico's honor would be diminished by selling any territory. Mexicans opposing open 
conflict with the United States, including President José Joaquín de Herrera, were viewed 
as traitors. When de Herrera considered receiving Slidell in order to peacefully negotiate 
the problem of Texas annexation, he was accused of treason and deposed.

Military opponents of President José Joaquín de Herrera considered Slidell's presence in 
Mexico City an insult. After a more nationalistic government under General Mariano 
Paredes y Arrillaga came to power, the new government publicly reaffirmed Mexico's 
claim to Texas, and Slidell left in a temper, convinced that Mexico should be "chastized." 

Mexico, which had never recognized Texas's independence, claimed the Nueces River — 
about 150 miles (240 km) north of the Rio Grande — as the border between Texas and 
Mexico. The United States, however, upheld Texas' claim to the land between the Nueces 
and the Rio Grande. The boundary claimed by Texas was established by the 1836 Treaty 
of Velasco that ended the Texas Revolution. Mexico argued that General Santa Anna 
signed the treaty under duress when he was held captive by the Texans, so it was invalid. 
Moreover, the Mexicans argued, Santa Anna had no authority to negotiate or sign a treaty, 
and the treaties were never ratified by the Mexican government. In 1846, after Texas was 
admitted into the Union, Polk sent troops under General Zachary Taylor to the Rio Grande 
to protect Texas from a threatened Mexican invasion (Bauer; 6, 17-18).

Taylor ignored Mexican demands to withdraw to the Nueces and began constructing a 
make-shift fort (later known as Fort Brown) on the banks of the Rio Grande opposite the 
Mexican town of Matamoros. Mexican forces under General Mariano Arista prepared for 
war.

On April 24, 1846, a 2,000-strong Mexican cavalry detachment attacked a 63-man U.S. 
patrol that was sent into the contested territory north of the Rio Grande and south of the 
Nueces River. The Mexican cavalry succeeded in routing the patrol, killing 11 U.S. soldiers 
in what later became known as the Thornton Affair, after the slain U.S. officer who was in 
command. A few survivors escaped and returned to Fort Brown.

On May 3, Mexican artillery at Matamoros opened fire on Fort Brown, which replied with its 
own guns. The bombardment continued for five days and expanded as the Mexican forces 
gradually surrounded the fort. Two U.S. soldiers were killed during the bombardment, 
including Jacob Brown, after whom the fort was later named.

On May 8, Zachary Taylor arrived with 2,400 troops to relieve the fort. However, Arista 
rushed north and intercepted him with a force of 3,400 at Palo Alto. The Americans used 
a new artillery method named flying artillery — a mobile light artillery that was mounted 
on horse carriages, with all cannoneers mounted as well. U.S. artillery had a devastating 
effect on the Mexican Army. The Mexicans responded with cavalry skirmishes and its 
own artillery. The U.S. flying artillery somewhat demoralized the Mexican side, and they 
felt the need to find a terrain more to their advantage. They retreated to the far side of a 
dry riverbed (resaca) during the night, which provided a natural fortification, but they also 
scattered their troops so that communication was difficult. During the Battle of Resaca 
de la Palma the next day, the two sides engaged in vicious hand-to-hand fighting. The 
U.S. cavalry managed to capture the Mexican artillery, leading the Mexican side to 
retreat—a retreat that turned into a rout. Because of the terrain and the dispersion of his 
troops, Arista found it impossible to rally his forces. Mexican casualties were heavy, and 
the Mexicans were forced to abandon their artillery and baggage. Fort Brown inflicted 
further casualties as the withdrawing troops passed by them and swam across the Rio 
Grande where many drowned.

By then, Polk had received word of the Thornton Affair and added this to the rejection of 
Slidell as the casus belli. A message to Congress on May 11, 1846, stated that Mexico 
had "invaded our territory and shed American blood upon the American soil." A joint 
session of Congress approved the declaration of war, with southern Democrats in strong 
support because they saw annexation of Mexico as an opportunity to increase the 
number of slave states. Sixty-seven Whigs voted against the war on a key slavery 
amendment, but on the final passage only 14 Whigs voted no, including Reps. Abraham 
Lincoln and John Quincy Adams. The United States declared war on Mexico on May 13, 
1846, and Mexico officially declared war on July 7 (sometimes the manifest from President 
Paredes on May 23 is construed as the declaration of war, but only the Mexican congress 
had that power).

Whigs in both the North and the South generally opposed the war, while most Democrats 
supported it. Whig Congressman Abraham Lincoln contested the causes for the war, and 
demanded to know the exact spot on which Thornton had been attacked and U.S. blood 
had been shed. He was quoted as saying "Show me the spot." Whig leader Robert Toombs 
of Georgia declared:

"This war is a nondescript.... We charge the President with usurping the war-making 
power... with seizing a country... which had been for centuries, and was then in the 
possession of the Mexicans.... Let us put a check upon this lust of dominion. We had 
territory enough, Heaven knew." [Beveridge 1:417] 
Northern abolitionists attacked the war as an attempt by slave-owners — frequently 
referred to as "the Slave Power" — to expand the grip of slavery and thus assure their 
continued influence in the federal government. Acting on his convictions, Henry David 
Thoreau was jailed for his refusal to pay taxes to support the war, and penned his famous 
essay, Civil Disobedience.

Former President John Quincy Adams also expressed his belief that the war was 
fundamentally an effort to expand slavery. In response to such concerns, Democratic 
Congressman David Wilmot introduced the Wilmot Proviso, which aimed to prohibit 
slavery in any new territory acquired from Mexico. Wilmot's proposal did not pass Congress, 
but it spurred further hostility between the factions.

After the declaration of war, U.S. forces invaded Mexican territory on two main fronts. 
The U.S. war department sent a cavalry force under Stephen W. Kearny to invade western 
Mexico from Fort Leavenworth, reinforced by a Pacific fleet under John D. Sloat. This was 
done primarily because of concerns that Britain might also attempt to occupy 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.

Letter from a Naval surgeon on board the frigate "Potomac" en route to Mexico

A young Navy assistant surgeon, Oscar F. Baxter, a native of North Carolina, when on his 
way to Vera Cruz during the Mexican War, wrote a letter to his fiancée. The letter was dated 
October 1, 1846 and was posted from Pensacola, Florida when his ship the frigate 
"Potomac" made a stop at the Navy yard there. In it he reported that there had been a 
lot of scurvy among the men on the ship, but the worst seemed to be over. But another 
disease was causing him great stress: yellow fever, which had afflicted some on the ship 
and about forty more workers at the Pensacola Navy yard (including the surgeon there, for 
whom Dr. Baxter had to fill in).

He goes on to say that he has heard a "rumor" that the overtures of peace offered by our 
government have come. He was happy to report that he anticipated, in several months' 
time, to return to the United States to take an examination, which if passed, would promote 
him from assistant surgeon to surgeon; such promotion would raise his annual salary from 
$1,028 to $1,273.

He also reports:

The blockading squadron off Vera Cruz has recently captured several rich prizes--the value 
of the two last is estimated at $150,000. They will be brought in and be judged by a Court 
of Admiralty whether they are legal prizes or not.

After all of that, he includes the following in his letter:

A man by the name of Samuel Jackson, seaman on board of the St. Mary's (a sister ship 
to the "Potomac" in the squadron en route to Mexico) has been sentenced to death by a 
Court Martial recently held upon the charges preferred against him for mutiny. The 
Commodore has approved the sentence and the day has been appointed for carrying it into 
effect. An example of the kind becomes sometimes an act of humanity. If he be let off, a 
dozen may ultimately may have to suffer his sentence carried into effect. It is possible the 
Commodore may reprieve him. If he does it will be a death blow to the discipline of the 
Squadron.

Actually, Jackson had already been executed on September 21, 1846, according to the 
account published in The Daybook included below. Evidently, Dr. Baxter had heard of the 
incident on his way to Pensacola, but had not yet learned of the execution when he wrote 
his letter on October 1st.

(The actual letter referred to above is in the possession of Dr. Baxter's great-grandson, who 
lives in Baltimore County, Maryland. Later, after North Carolina seceded from the Union at 
the time of the Civil War, Dr. Baxter became a surgeon in the Confederate army. Excerpts 
from several letters to his twelve-year-old daughter in 1864 from the field of battle at Chaffin's 
Bluff in Virginia (at which time he was a widower) describe the intense fighting going on 
around his field hospital and the large number of badly-wounded men, both Confederate 
and Union, that he had to treat.)

There is no account of this act of mutiny in Mutiny: A History of Naval Insurrection, by 
Leonard F. Guttridge, published in 1992 by Naval Institute Press. However, it is referred 
to in The Daybook (Vol. 9 Issue 4, undated, p. 14) a publication of the Hampton Roads 
Naval Museum.

Several weeks into the (Mexican) war, discipline continued to be a problem...throughout 
the squadron. Despite weekly floggings, officers and sailors continue to violate basic rules 
of discipline...Tired of the chaos, (the squadron commander) decided to make an example 
of one sailor. The unlucky fellow was Seaman Samuel Jackson of St. Mary’s. Jackson had 
assaulted his division officer. Though everyone in the squadron, including the lieutenant 
who was attacked, thought it to be excessive, an execution went forward. Rev. Taylor 
made many trips over to St. Mary’s to see the condemned man and to convert him to 
Christianity before his death...on the morning of September 21, Jackson was hung from 
the yardarm in front of the entire squadron. While many disagreed with (the squadron 
commander's) decision, there were far fewer discipline problems for the rest of the war.

When the US declared war against Mexico, on May 13, 1846, it took almost two months 
(mid-July 1846) for definite word of war to get to California. U.S. consul Thomas O. Larkin, 
stationed in Monterey, on hearing rumors of war tried to keep peace between the U.S. and 
the small Mexican military garrison commanded by José Castro. U.S. Army captain John 
C. Frémont with about 60 well-armed men had entered California in December 1845 and 
was making a slow march to Oregon when they received word that war between Mexico 
and the U.S. was imminent. 

On June 15, 1846, some 30 settlers, mostly U.S. citizens, staged a revolt and seized the 
small Mexican garrison in Sonoma. They raised the "Bear Flag" of the California Republic 
over Sonoma. It lasted one week until the U.S. Army, led by Fremont, took over on June 
23. The California state flag today is based on this original Bear Flag, and still contains 
the words "California Republic."

Commodore John Drake Sloat, on hearing of imminent war and the revolt in Sonoma, 
ordered his naval forces to occupy Yerba Buena (present San Francisco) on July 7 and 
raise the American flag. On July 15, Sloat transferred his command to Commodore 
Robert F. Stockton, a much more aggressive leader, who put Frémont's forces under 
his orders. On July 19, Frémont's "California Battalion" swelled to about 160 additional 
men from newly arrived settlers near Sacramento, and he entered Monterey in a joint 
operation with some of Stockton's sailors and marines. The word had been received — 
the war was official. The U.S. forces easily took over the north of California; within days 
they controlled San Francisco, Sonoma, and Sutter's Fort in Sacramento.

In Northern California, Mexican General José Castro and Governor Pío Pico fled to Mexico . 
When Stockton's forces, sailing south to San Diego, stopped in San Pedro, he dispatched 
50 US Marines, and entered Los Angeles unresisted on August 13, 1846, known as the 
Siege of Los Angeles, the nearly bloodless conquest of California seemed complete. 
Stockton, however, left too small a force in Los Angeles, and the Californios, acting on 
their own and without help from Mexico, led by José Mariá Flores , forced the American 
garrison to retreat in late September. More than 300 reinforcements sent by Stockton, 
led by U.S. Navy Captain William Mervine, were repulsed in the Battle of Dominguez 
Rancho, October 7 through October 9, 1846, near San Pedro, where 14 U.S. Marines 
were killed. The rancho vaqueros, banded together to defend their land, fighting as 
Californio Lancers, became a force to deal with the Americans had not planned on. 
Meanwhile, General Stephen W. Kearny, with a squadron of 139 dragoons, finally reached 
California after a grueling march across New Mexico, Arizona and the Sonora desert, on 
December 6, 1846, and was defeated by the Californio Lancers at the Battle of San 
Pasqual near San Diego, California, where 22 of Kearny's troops were killed.

Stockton rescued Kearny's retreating forces and later, with their re-supplied, combined 
force, marched north from San Diego, entering the Los Angeles area on January 8, 1847, 
linking up with Frémont's men. With U.S. forces totaling 660 soldiers and marines, they 
fought and defeated the 160 man Californio force in the decisive Battle of Rio San Gabriel, 
and the next day, January 9, 1847, they fought the Battle of La Mesa. On January 12, 
1847, the last significant body of Californios surrendered to U.S. forces. That marked 
the end of the War in California. On January 13, 1847, the Treaty of Cahuenga was signed.

On January 28, 1847, U.S. Army Lieutenant William Tecumseh Sherman and his army 
unit arrived in Monterey, California as U.S. forces in the pipeline continued to stream 
into California. On March 15, 1847, Col. Jonathan D. Stevenson’s Seventh Regiment of 
New York Volunteers of about 900 men started arriving in California. All of these men 
were in place when word went out that gold was discovered in California, January 1848.

The defeats at Palo Alto and Resaca de la Palma caused political turmoil in Mexico, 
turmoil which Antonio López de Santa Anna used to revive his political career and 
return from self-imposed exile in Cuba. He promised the U.S. troops that if allowed to 
pass through their blockade, he would negotiate a peaceful conclusion to the war and 
sell the New Mexico and California territories to the United States. Once he arrived in 
Mexico, however, he reneged and offered his military skills to the Mexican government. 
After he had been appointed general he reneged again and seized the presidency.

2,300 U.S. troops led by Taylor crossed the Rio Grande (Rio Bravo) after some initial 
difficulties in obtaining river transport. He occupied the city of Matamoros, then Camargo 
(where while waiting the soldiery suffered the first of many problems with disease) and 
then proceeded south and besieged the city of Monterrey. This Battle of Monterrey was 
a hard fought battle during which both sides suffered serious losses. The American light 
artillery was ineffective against the stone fortifications of the city. The Mexican forces 
were under General Pedro de Ampudia. A U.S. infantry division and the Texas Rangers 
captured four hills to the west of the town and with them heavy cannon. That lent the 
U.S. soldiers the strength to storm the city from the west and east. Once in the city, 
U.S. soldiers fought house to house: each was cleared by throwing lighted shells, 
which worked like grenades. Eventually, these actions drove and trapped Ampudia's 
men into the city's central plaza, where howitzer shelling forced Ampudia to negotiate. 
Taylor agreed to allow the Mexican Army to evacuate and to an 8-week armistice in 
return for the surrender of the city. Under pressure from Washington, Taylor broke the 
armistice and occupied the city of Saltillo, southwest of Monterrey. Santa Anna 
blamed the loss of Monterrey and Saltillo on Ampudia and demoted him to command 
a small artillery battalion.

On February 22, 1847, Santa Anna personally marched north to fight Taylor with 20,000 
men. Taylor, with 4,600 men, had entrenched at a mountain pass called Buena Vista. 
Santa Anna suffered desertions on the way north and arrived with 15,000 men in a tired 
state. He demanded and was refused surrender of the U.S. army; he attacked the next
morning. Santa Anna flanked the U.S. positions by sending his cavalry and some of his 
infantry up the steep terrain that made up one side of the pass, while a division of infantry 
attacked frontally along the road leading to Buena Vista. Furious fighting ensued during 
which the U.S. troops were almost routed, but were saved by artillery fire against a 
Mexican advance at close range by Captain Braxton Bragg, and a charge by the mounted 
Mississippi Riflemen under Jefferson Davis. Having suffered discouraging losses, Santa 
Anna withdrew that night, leaving Taylor in control of Northern Mexico. Polk distrusted Taylor, 
whom he felt had shown incompetence in the Battle of Monterrey by agreeing to the armistice, 
and may have considered him a political rival for the White House. Taylor later used the Battle 
of Buena Vista as the centerpiece of his successful 1848 presidential campaign.

Rather than reinforce Taylor's army for a continued advance, President Polk sent a second 
army under General Winfield Scott, which was transported to the port of Veracruz by sea, 
to begin an invasion of the Mexican heartland. Scott performed the first major amphibious 
landing in the history of the United States in preparation for the Siege of Veracruz. A group 
of 12,000 volunteer and regular soldiers successfully offloaded supplies, weapons and 
horses near the walled city. Included in the invading force were Robert E. Lee, George 
Meade, Ulysses S. Grant, and Thomas "Stonewall" Jackson. The city was defended by 
Mexican General Juan Morales with 3,400 men. Mortars and naval guns under Commodore 
Matthew C. Perry were used to reduce the city walls and harass defenders. The city replied 
as best it could with its own artillery. The effect of the extended barrage destroyed the will 
of the Mexican side to fight against a numerically superior force, and they surrendered the 
city after 12 days under siege. U.S. troops suffered 80 casualties, while the Mexican side 
had around 180 killed and wounded, about half of whom were civilian. During the siege, the 
U.S. side began to fall victim to yellow fever.

Scott then marched westward toward Mexico City with 8,500 healthy troops, while Santa 
Anna set up a defensive position in a canyon around the main road at the halfway mark to 
Mexico City, near the hamlet of Cerro Gordo. Santa Anna had entrenched with 12,000 
troops and artillery that were trained on the road, along which he expected Scott to appear. 
However, Scott had sent 2,600 mounted dragoons ahead, and the Mexican artillery 
prematurely fired on them and revealed their positions. Instead of taking the main road, 
Scott's troops trekked through the rough terrain to the north, setting up his artillery on 
the high ground and quietly flanking the Mexicans. Although by then aware of the positions 
of U.S. troops, Santa Anna and his troops were unprepared for the onslaught that followed. 
The Mexican army was routed. The U.S. army suffered 400 casualties, while the Mexicans 
suffered over 1,000 casualties and 3,000 were taken prisoner.

In May, Scott pushed on to Puebla, the second largest city in Mexico. Because of the 
citizens' hostility to Santa Anna, the city capitulated without resistance on May 1. Mexico 
City was laid open in the Battle of Chapultepec and subsequently occupied.

Winfield Scott became an American national hero after his victories in the Mexican War, 
and later became military governor of occupied Mexico City.

The novel, Gone for Soldiers, by Jeff Shaara, explains a great deal of General Scott's 
campaign, from the point of view of three characters. These characters were Colonel 
Robert E. Lee, General Winfield Scott, and Mexican Dictator Antonio López de Santa 
Anna.

The Treaty of Guadalupe Hidalgo, signed on February 2, 1848 by American diplomat 
Nicholas Trist, ended the war and gave the U.S undisputed control of Texas, established 
the U.S.-Mexican border of the Rio Grande River, and ceded to the United States California, 
Nevada, Utah, and parts of Colorado, Arizona, New Mexico, and Wyoming. In return, 
Mexico received US $15,000,000. This exchange is known as the Mexican Cession. 
Mexicans living in the conquered lands could choose to return to Mexico or stay and 
become American citizens. Article X was stricken from the treaty before it was ratified 
by the U.S. Senate. These articles promised that the United States would recognize 
Mexican and Spanish land grants.

In 1853, in what became known as The Gadsden Purchase, the United States paid an 
additional $10 million to Mexico to purchase land in what is now southern Arizona and 
southern New Mexico for the construction of a southern route for a transcontinental 
railroad. The purchase was also designed to further compensate Mexico for the lands 
taken by the U.S. after the Mexican-American War.

Mexico lost more than 500,000 square miles (about 1,300,000 square km) of land, 
almost half of its territory. The annexed territories contained about 1,000 Mexican 
families in California and 7,000 in New Mexico. A few moved back to Mexico; the great 
majority remained in the US. Descendants of these Mexican families have risen to 
prominence in American life, such as United States Senator Ken Salazar, and his 
brother, U.S. Rep. John Salazar, both from Colorado.

A month before the end of the war, Polk was criticized in a United States House of 
Representatives amendment to a bill praising Major General Zachary Taylor for "a war 
unnecessarily and unconstitutionally begun by the President of the United States." 
This criticism, in which Congressman Abraham Lincoln played an important role, 
followed congressional scrutiny of the war's beginnings, including factual challenges 
to claims made by President Polk. The vote followed party lines, with all Whigs 
supporting the amendment. Lincoln's attack haunted his future campaigns in the heavily 
Democratic state of Illinois, and was cited by enemies well into his presidency. The 
stand did not cost Lincoln his Congressional seat in Illinois' Seventh Congressional 
District; the district was the only place in Illinois where a Whig could win high office, 
and party leaders agreed to one-term limits for Whig representatives there. Lincoln was 
succeeded by a Democrat, but the Seventh Congressional District voted for Zachary 
Taylor, a Whig, that fall.

In much of the United States, victory and the acquisition of new land brought a surge of 
patriotism (the country had also acquired the southern half of the Oregon Country in 
1846 through a treaty with Great Britain). Victory seemed to fulfill citizens' belief in their 
country's Manifest Destiny. While Whig Ralph Waldo Emerson rejected war "as a means 
of achieving America's destiny," he accepted that "most of the great results of history are 
brought about by discreditable means." Although the Whigs had opposed the war, they 
made Zachary Taylor their presidential candidate in the election of 1848, praising his 
military performance while muting their criticism of the war itself.

In the 1880s, Ulysses S. Grant, who had served under Taylor's command, called the 
conflict an evil war that had brought God's punishment on the United States in the form 
of the American Civil War:

The Southern rebellion was largely the outgrowth of the Mexican war. Nations, like 
individuals, are punished for their transgressions. We got our punishment in the most 
sanguinary and expensive war of modern times. 

In the "Personal Memoirs of Ulysses S. Grant" published in 1885, Grant recalled his 
actions in the Mexican War with regret:

Generally, the officers of the army were indifferent whether the annexation was 
consummated or not; but not so all of them. For myself, I was bitterly opposed to the 
measure, and to this day regard the war, which resulted, 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. 

Many of the generals of the latter war had fought in the former, including Grant, George 
B. McClellan, Ambrose Burnside, Stonewall Jackson, James Longstreet, George Meade, 
and Robert E. Lee, as well as the future Confederate President Jefferson Davis. In 
Mexico City's Chapultepec Park, the Monument to the Heroic Cadets commemorates 
the heroic sacrifice of six teenaged military cadets who fought to their deaths rather 
than surrender to American invaders during the Battle of Chapultepec Castle on 
September 18, 1847. The monument is an important patriotic site in Mexico. On 
March 5, 1947, nearly one hundred years after the battle, U.S. President Harry S. 
Truman placed a wreath at the monument and stood for a moment of silence.

Although 13,000 U.S. soldiers died during the course of the Mexican War, only about 
1,700 were killed in combat. 90% died of disease, such as yellow fever. Mexican 
casualties are estimated at 25,000.

One of the contributing factors to loss of the war by Mexico was the inferiority of their 
weapons. The Mexican army was using British muskets from the Napoleonic Wars, 
while U.S. troops had the latest U.S. manufactured rifles. Furthermore, Mexican troops 
were trained to fire with their musket held loosely at hip-level, while U.S. 
soldiers used the much more accurate method of butting the rifle up to the shoulder and 
taking aim along the barrel.

Another factor that contributed to victory for the United States was the fact that the 
Mexican Army was separated by two factions ("centralistas" and "republicanos") who 
were against each other in a civil war.

The Saint Patrick's Battalion (San Patricios), was a group of several hundred immigrant 
soldiers, the majority Irish, who deserted the U.S. Army because of ill-treatment or 
sympathetic leanings to fellow Mexican Catholics, joined the Mexican army. Most were 
killed in the Battle of Churubusco; about 100 were captured by the U.S. and roughly half 
were hanged as deserters.

The last surviving U.S. veteran of the conflict, Owen Thomas Edgar, died on September 
3, 1929, at age 98.

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 more than 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 result of Nicholas Trist's unauthorized negotiations. 
It was 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 of Texas north of the Rio Grande formalized the addition of 3.1 million 
km2 (1.2 million mi2) 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.





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