By Roy Cook

The war between the United States and Mexico had two basic causes.

1.      First, the desire of the U.S. to expand across the North American continent, the policy of Manifest Destiny, to the Pacific Ocean caused conflict with all of the U.S. neighbors; from the British in Canada and Oregon to the Mexicans in the southwest and, of course, with the Native Americans, many on U.S.  treaty secured lands.

2.      The second basic cause of the war with Mexico was the Texas War of Independence and the subsequent annexation of that area to the United States.

After the beginning of hostilities, the U.S. military reported to the President and it became apparent to the Polk Administration that only a complete battlefield victory would end the war. Continued fighting in the dry deserts of northern Mexico convinced the United States that an overland expedition to capture of the enemy capital, Mexico City, would be hazardous and difficult. To this end, General Winfield Scott proposed what would become the largest amphibious landing in history, (at that time), and a campaign to seize the capital of Mexico. The Marine Corps still recognizes this landing in the first line of the Corps' hymn: From the Halls of Montezuma.
One interesting aspect of the war involves the fate of U.S. Army deserters of Irish origin who joined the Mexican Army as the Batallón San Patricio (Saint Patrick's Battalion). This group of Catholic Irish immigrants rebelled at the abusive treatment by Protestant, American-born officers and at the treatment of the Catholic Mexican population by the U.S. Army. At this time in American history, Catholics were an ill-treated minority, and the Irish were an unwanted ethnic group in the United States. In September 1847, the U.S. Army hanged sixteen surviving members of the San Patricios as traitors. To this day, they are considered heroes in Mexico.

The story of this famed group begins with the founder and chief conspirator, John Riley, a Galway native born in 1817. Riley deserted from the British army while stationed in Canada and went to Michigan, where he later enlisted in the US Army in 1845. He was able to defect to the Mexican Army when his commander granted him permission to cross into Mexico to attend mass. It was there, in Matamoros, Riley joined the Mexican Army as a lieutenant, which resulted in his pay rising from seven dollars per month to 57 dollars per month. While desertion from the US armed forces was punishable by death, Riley was not deterred in capitalizing on the dis-satisfaction of many Irish-born US soldiers with their adopted country. Aided by his second-in-command, Patrick Dalton, who was from the parish of Tirawley, near Ballina, County Mayo, Riley at first was successful in persuading 48 Irishmen to defect, and these men made up the original Saint Patrick's Battalion. In addition to more Irishmen joining, they welcomed other foreign-born US deserters, as well as American-born deserters. Also, some Irish-born civilian residents of Mexico were persuaded to join the struggle. Even when the number of San Patricios rose to more than 200, Irish-born members still represented nearly 50 per cent.

Looking back, to the motivation for the policy of Manifest Destiny, we need to examine President Jefferson's acquisition of the right to treat with the Indian Nations for land in Louisiana Territory in 1803, Americans illegally migrated westward in ever increasing numbers, very often into lands not belonging to the United States. By the time President Polk came to office in 1845, this idea, based on racist principals called "Manifest Destiny", had taken root among the American people, and President Polk was a firm believer in the idea of expansion. The belief that the U.S. basically had a Euro-centered God-given right to occupy and "civilize" the whole continent gained favor as more and more Americans invaded the western lands. The fact that most of those areas already had Tribal people living upon them was usually ignored, with the attitude that democratic English-speaking America, with its high ideals and Protestant Christian ethics, would do a better job of running things than the Native Americans or Spanish-speaking Catholic Mexicans.

Manifest Destiny did not necessarily call for violent expansion if the land can be bought cheap. In both 1835 and 1845, the United States offered to purchase California from Mexico, for $5 million and $25 million, respectively. The Mexican government refused the opportunity to sell half of its country to Mexico's most dangerous neighbor. Many Americans opposed what they called "Mister Polk's War." Whig Party members and abolitionists in the North believed that slave-owners and Southerners in Polk's administration had planned the war. They believed the South wanted to win Mexican territory for the purpose of spreading and strengthening slavery. This opposition troubled President Polk. But he did not think the war would last long. He thought the US could quickly force Mexico to sell him the territory he wanted.

Polk secretly sent a representative to former Mexican dictator Santa Ana, who was living in exile in Cuba. Polk's representative said the United States wanted to buy California and some other Mexican territory. Santa Ana said he would agree to the sale, if the United States would help him return to power. President Polk ordered the US Navy to let Santa Ana return to Mexico. American ships that blocked the port of Vera Cruz permitted the Mexican dictator to land there. Once Santa Ana returned, he failed to honor his promises to Polk. He refused to end the war and sell California. Instead, Santa Ana organized an army to fight the United States.

Not all American westward migration was unwelcome. In the 1820's and 1830's, Mexico, newly independent from Spain, needed settlers in the under-populated northern parts of the country. An invitation was issued for people who would take an oath of allegiance to Mexico and convert to Catholicism, the official religion. Thousands of Americans took up the offer and moved, often with slaves, to the Mexican province of Tejas (texas). Soon however, many of the new "Texicans" or "Texians" were unhappy with the way the government in Mexico City tried to run the province. In 1835, the Tejanos revolted, and after several bloody battles, the Mexican President, Santa Anna, was forced to sign the Treaty of Velasco in 1836  This treaty gave Tejas (texas) its independence, but many Mexicans refused to accept the legality of this document, as Santa Anna was a prisoner of the Tejanos at the time. The Republic of Tejas (texas) and Mexico continued to engage in border fights and many people in the United States openly sympathized with the U.S.-born Texans in this conflict. As a result of the savage frontier fighting, the American public developed a very negative stereotype against the Mexican people and government. Partly due to the continued hostilities with Mexico, Texas decided to join with the United States, and on July 4, 1845, the annexation gained approval from the U.S. Congress.

Official Military campaign accounts: The "Army of Observation" commanded by General Zachary Taylor was deployed to Corpus Christi, at the mouth of the Nueces River, to protect newly annexed Texas in the summer of 1845. The force consisted of 5 regiments of infantry, 1 regiment of dragoons, and 16 companies of artillery. After the beginning of hostilities, the U.S. military embarked on a three-pronged strategy designed to seize control of northern Mexico and force an early peace. Two American armies moved south from Texas, while a third force under Colonel Stephen Kearny travelled west to Sante Fe, New Mexico and then to California. In a series of battles at Palo Alto and Resaca de Palma (near current-day Brownsville, Texas), the army of General Zachary Taylor defeated the Mexican forces and began to move south after inflicting over a thousand casualties. In July and August of 1846, the United States Navy seized Monterey and Los Angeles in California. In September, 1846, Taylor's army fought General Ampudia's forces for control of the northern Mexican city of Monterey in a bloody three-day battle. Following the capture of the city by the Americans, a temporary truce ensued which enabled both armies to recover from the exhausting Battle of Monterey. During this time, former President Santa Anna returned to Mexico from exile and raised and trained a new army of over 20,000 men to oppose the invaders. Despite the losses of huge tracts of land, and defeat in several major battles, the Mexican government refused to make peace.

On March 9, 1847, General Scott landed with an army of 12,000 men on the beaches near Veracruz, Mexico's most important eastern port city. From this point, from March to August, Scott and Santa Anna fought a series of bloody, hard-fought battles from the coast inland toward Mexico City.

Churubusco, 20 August 1847. Santa Anna promptly made another stand on Churubusco where he suffered a disastrous defeat in which his total losses for the day "killed, wounded, and especially deserters" were probably as high as 10,000. Scott estimated the Mexican losses at 4,297 killed and wounded, and he took 2,637 prisoners. Of 8,497 Americans engaged in the almost continuous battles of Contreras and Churubusco, 131 were killed, 865 wounded, and about 40 missing.

Scott proposed an armistice to discuss peace terms. Santa Anna quickly agreed; but after two weeks of fruitless negotiations it became apparent that the Mexicans were using the armistice merely for a breathing spell. On 6 September Scott broke off discussions and prepared to assault the capital. To do so, it was necessary to take the citadel of Chapultepec, a massive stone fortress on top of a hill about a mile outside the city proper. Defending Mexico City were from 18,000 to 20,000 troops, and the Mexicans were confident of victory, since it was known that Scott had barely 8,000 men and was far from his base of supply.

Molino del Rey, 8 September 1847. On 8 September 1847, the Americans launched an assault on Molino del Rey, the most important outwork of Chapultepec. It was taken after a bloody fight, in which the Mexicans suffered an estimated 2,000 casualties and lost 700 as prisoners, while perhaps as many as 2,000 deserted. The small American force had sustained comparatively serious losses "124 killed and 582 wounded" but they doggedly continued their attack on Chapultepec, which finally fell on 13 September 1847. American losses were 138 killed and 673 wounded during the siege of the fortress. Mexican losses in killed, wounded, and captured totaled about 1,800. The fall of the citadel brought Mexican resistance practically to an end. Authorities in Mexico City sent out a white flag on 14 September 1847. Santa Anna abdicated the Presidency, and the last remnant of his army, about 1,500 volunteers, was completely defeated a few days later while attempting to capture an American supply train.

 On 2 February 1848, the Treaty of Guadalupe Hidalgo was signed, ratified in the U.S. Senate on 10 March 1848, by the Mexican Congress in May. The treaty called for the annexation of the northern portions of Mexico to the United States. On 1 August 1848 the last American soldier departed for home.

 In return, the U.S. agreed to pay $15 million to Mexico as compensation for the seized territory. This "seized Mexican territory" is the most controversial issue in the Southwest history. Almost never delineated is the actual territory controlled and not just claimed by Mexico or previously by Spain.

The bravery of the individual Mexican soldier goes a long way in explaining the difficulty the U.S. had in conducting the war. Mexican military leadership was often lacking, at least when compared to the American leadership. And in many of the battles, the superior cannon of the U.S. artillery divisions and the innovative tactics of their officers turned the tide against the Mexicans. The war cost the United States over $100 million, and ended the lives of 13,780 U.S. military personnel. America had defeated its weaker and somewhat disorganized southern neighbor, but not without paying a terrible price.

 This divisive legacy is so often overlooked in our general education.

1. Despite early popularity at home, the war was marked by the growth of a loud anti-war movement that included such noted Americans as Ralph Waldo Emerson, former president John Quincy Adams and Henry David Thoreau. The center of anti-war sentiment gravitated around New England, and was directly connected to the movement to abolish slavery. Texas became a slave state upon entry into the Union.

 2. While it is widely perceived in Mexico that the San Patricios defected solely on the issue of religion, this myth is examined in a later chapter of Robert Miller's book: Shamrock and Sword, entitled "Why they Defected". The fact that there was rampant anti-Catholic bigotry in the US at that time does not play as great a role in the formation of the unit as is believed in Mexico. Miller states that the religious bond was not a main reason why many defected. The attractive offer of high pay in the Mexican Army and the promise of land grants to defectors after the war outweighed the fraternal bond over religion, according to Miller.

A main reason for their hero status in Mexico is derived from their exemplary performance in the battlefield. The San Patricios ultimately suffered severe casualties at the famous battle at Churubusco, which is considered the Waterloo for the Mexican Army in this war. Mexican President Antonio Lopez Santa Anna, who also commanded the armed forces, stated afterwards that if he had commanded a few hundred more men like the San Patricios, Mexico would have won that ill-famed battle.

Each San Patricio soldier who deserted from the US side was interned after the war in Mexico and subsequently given an individual court-martial trial. Many of the Irish were set free, but some paid the ultimate price. Roughly half of the San Patricio defectors who were executed by the US for desertion were Irish. Those Irish who were released by American authorities did not return to the US; some stayed in Mexico while most returned to Ireland, including John Riley who, surprisingly, was spared execution.

Furthermore, Miller makes it clear that the Irish deserters of the Saint Patrick's Battalion were in no way representative of the Irish-born soldiers who made up one-fourth of all enlisted men in the US Army during the US-Mexican War. There were seventeen totally Irish companies who saw action in this war; many were highly decorated units such as the Emmet Guards from Albany, New York; the Jasper Greens of Savannah, Georgia; the Mobile Volunteers of Alabama; the Pittsburgh Hibernian Greens.

 In 1959, the Mexican government dedicated a commemorative plaque to the San Patricios across from San Jacinto Plaza in the Mexico City suburb of San Angel; it lists the names of all members of the battalion who lost their lives fighting for Mexico, either in battle or by execution. There are ceremonies there twice a year, on September 12, this is the anniversary of the executions, and on Saint Patric's Day. A major celebration was held there in 1983, when the Mexican government authorized a special commemorative medallion honoring the San Patricios.

The Infantry flag made by the nuns at San Luis Potosi is described as "The banner is of green silk, and on one side is a harp, surmounted by the Mexican coat of arns, with a scroll on which is painted 'Lebertad por Republica Mexicana". Underneath the harp is the motto "Erin Go Bragh'. (Ireland Forever) On the other side is a painting made to represent St. Patrick, his left hand a key and in his right a crook or staff resting upon a serpent.

This is the flag captured at Churubusco by the 14th US Infantry and later apparently taken to West Point and placed in the chapel. But, it did not survive because when President Truman returned the captured Mexican War flags it was not returned. The chapel was replaced sometime in the 1930's and by then the flag seems to have vanished.

3. In Mexico, a special day is remembered to celebrate the bravery of the teenaged military cadets at the military academy at Chapultepec Castle, which was attacked by Scott's army on September 13, 1847. "Dia de Los Niños Heroes de Chapultepec" (day of the boy heroes of Chapultepec), is commemorated every year on the anniversary of the battle.

Seated high on a hill, Chapultepec Castle had once been the resort of Aztec princes, hence its fame as the Halls of Montezuma. Since 1833, it had served as Mexico's military academy, and the cadets now fought side by side with seasoned soldiers in heroic defense of their castle and country. Six of the youths died, one clutching the Mexican flag to keep it from American hands. For their valor, they have been honored in annual celebrations as Los Niños Héroes. Ordered to retreat by their Commandant, these young cadets joined the fight- the boy heroes who are honored every year are the four teenaged cadets (Francisco Marquez, the youngest, was thirteen years old!) and their lieutenant squadron leader, Juan de la Barrera, (the oldest, age 20), who lost their lives in that battle.


Notes and sources:

1. Kohn, George C. Dictionary of Wars. New York: Facts On File Publications. 1986.

2. Eisenhower, John S.D. So Far From God: The U.S. War With Mexico 1846-1848. New York: Anchor Books, Doubleday. 1989.

3. Winders, Richard Bruce. Mr. Polk's Army. Texas A&M, 1997.

4. Frazier, Donald S., ed. The U.S. and Mexico at War: Nineteenth Century Expansionism and Conflict. Macmillan Library Reference, 1998.

5. Lee, R. "The History Guy: The Mexican-American War"

6. Miller, Robert R: Shamrock & Sword

7. /patricios.html