The Battle of Mexico City on September 13-14, 1847, between U.S. and Mexican forces caused Mexico to sue for peace and led to major territorial gains for the United States. U.S. president James K. Polk’s insistence on acquiring upper California was the cause of the Mexican-American War (1846-1848). The excuse for the war came in U.S. claims regarding the southern boundary of Texas.
Polk, who took office in March 1845, was a staunch proponent of Manifest Destiny and sought U.S. expansion west to the Pacific Ocean and south to at least the Rio Grande. For Polk, the goal was to secure California. This rich Mexican province had a population of only 6,000 white men and seemed ready for the taking. Polk feared that if the United States did not act, Britain or France might acquire California. Polk tried on several occasions to purchase California, but the Mexican government refused. When Polk’s efforts to stir up revolution in California failed, he baited Mexico into war over Texas.
U.S. settlers in the Mexican province of Texas had revolted in 1836 and gained their independence. The Republic of Texas was then admitted to the United States in February 1845. That July, Polk ordered U.S. Army units under Major General Zachary Taylor to the Nueces River, the southwestern border of Texas, supposedly to protect it from Mexican attack. In January 1846 after receiving word that the Mexican government refused to receive his emissary, Polk ordered Taylor to cross the Nueces River and occupy the left bank of the Rio Grande. This was in effect an act of war.
On April 25 a Mexican force crossed the Rio Grande and engaged in a cavalry skirmish with a troop of U.S. dragoons, inflicting several casualties. Polk immediately sent a message to Congress proclaiming that “Mexico has passed the boundary of the United States, has invaded our territory and shed American blood upon the American soil.” Congress responded with a declaration of war on May 13. On June 15 Polk negotiated a resolution of the Oregon Boundary dispute with Britain, thus covering his northern flank.
Both Mexico and the United States were confident of victory. The United States had 17 million people while Mexico had only 7 million, but the Mexican regular army was a large European-type establishment of 32,000 men. Polk had permitted Mexican general Antonio Lopez de Santa Anna, deposed after the loss of Texas, to return to Mexico from exile in Havana on the pledge that he would conclude the treaty that Polk sought. In September 1846 Santa Anna became president, and he was determined to fight.
The U.S. regular army numbered only 8,000 men. Congress authorized 50,000 volunteers and an increase in the size of the regular army to 15,000 men and eventually to 32,000. Mexico had virtually no navy, however, while the United States had 70 vessels. Control of the seas would be a key factor, enabling the United States to conduct offensive operations far from its home bases.
There were three major theaters of war: California, northern Mexico, and central Mexico. Fighting in California consisted of small-scale engagements, and by the end of 1846 U.S. forces were firmly in control there. Taylor crossed the Rio Grande into northern Mexico in late May 1846 and then during September 21-23 secured the major city of Monterrey. Taylor’s grandstanding alarmed Polk, however, who saw in him a potential political rival. Polk therefore turned to Major General Winfield Scott. Scott now drew off much of Taylor’s force, leaving him only 5,000 men, many of them untrained volunteers.
Learning of this situation, Santa Anna hurried north from Mexico City. Taylor received much-needed reinforcements from Brigadier General John E. Wood but was still badly outnumbered in the February 22-23, 1847, Battle of Buena Vista. Taylor nonetheless defeated Santa Anna, who then withdrew south to meet Scott.
Scott planned to win the war by marching on Mexico City from Veracruz, the capital’s port. The U.S. Navy made this possible when on March 9, 1847, it landed Scott’s entire army of 12,000 men along with their artillery, horses, and supplies near Veracruz. The city surrendered on March 27. At the same time, Mexico City was undergoing another revolution. As recent scholarship makes clear, internal Mexican discord greatly assisted the U.S. military effort throughout.
Scott’s subsequent campaign was brilliant. He was forced to proceed with little more than half the number of men he had requested and was constantly hampered by jealous subordinates. He was often forced to live off the land and make do with captured ammunition. Scott’s orchestration of the 260-mile-march from Veracruz to Mexico City ranks him among the greatest American military commanders. Scott wisely insisted on amicable relations with the Mexicans, requiring his men to pay for horses and food. This helped secure the army’s rear areas during the march.
During April 17-18, 1847, Scott turned a strong Mexican blocking position at Cerro Gordo. Reaching and taking Puebla, he rested his army there for several months, replenishing it with volunteers to replace those whose enlistments had expired. The army was brought up to 11,000 men, but 30,000 Mexican troops still opposed them. With his supply lines now under constant harassment from the Mexican Army, Scott cut free of his base to advance on Mexico City, living off the land.
On August 20 the Americans fought a major battle at the Churubusco River, the last natural barrier to Mexico City. The Americans lost more than 1,000 men killed or wounded, while the Mexicans lost perhaps 7,000 men, including those captured. The well-handled American artillery was a major factor in the outcome, as it was in many other battles during the war. On August 23 Scott granted the Mexicans an armistice in the hope that this would bring reflection and meaningful peace negotiations, but Mexican officials balked at Polk’s terms, and Santa Anna renewed the fight. On September 8 U.S. forces won the Battle of Molino del Rey in a bloody assault on an entrenched Mexican position. U.S. losses were about 800 men, while the Mexicans suffered 2,700 casualties.
Scott now had 7,180 men for the final assault on the Mexican capital against perhaps 15,000 Mexican defenders. The main assault on the city came a few days later on September 12. Mexico City was guarded in part by Chapultepec Castle, which was being used as a military academy. Scott preceded infantry assault with an all day artillery barrage on September 12. The next day, September 13, the 4th Division, under John A. Quitman, spearheaded the attack against Chapultepec and carried the castle. Future Confederate generals George E. Pickett and James Longstreet participated in the attack. Serving in the Mexican defense were the cadets later immortalized as Los Niños Héroes (the “Boy Heroes”). The Mexican forces fell back from Chapultepec and retreated within the city.
Quitman’s Division made its way down the Belén Causeway towards the Belén Gate, defended by General Terres & Colonel Garay with the 2d Mexico Activos (200 men) and 3 guns ( 1-12 lbs. & 2-8 lbs.), while Worth’s Division further to the north made its way up La Verónica Causeway towards the San Cosme Gate, defended by General Rangel’s Infantry Brigade (Granaderos Battalion (Adj. A. Manero), 1st Light(Comdte. L. Marquez), part 3d Light (Lt.Col. M.M. Echeagaray)and parts of Matamoros, Morelia and Santa Ana Battalions (Col. J.V. Gonzalez) with 3 guns (1-12 lb, 1-8 lb. and 1 howitzer 24 lbs. Quitman was merely supposed to make a feint towards the city, but he pushed forward his whole division and broke through the defenses. Santa Anna arrived at the Belén Gate in a fury and relieved the front commander. Worth’s Division in the meantime had a slow start against the Mexicans after beating off a Mexican cavalry attack. When he reached San Cosme, he found its defenses ill prepared, but the Mexicans defending it put up a good fight before falling back. Ulysses S. Grant found his way into the action along the causeway on Worth’s front and helped in hoisting a cannon into the belltower of a nearby church. From this spot Grant fired into the defenders below. When the fighting subsided on all fronts, both gates had fallen and the Mexicans had withdrawn into the city. Other gates defended were: San Antonio by General M. Martínez ( 3d & 4th Ligero & 11th Line with 10 guns ) before withdrawing; Nino Perdido by the National Guards and 2 guns; and San Lázaro, Guadalupe and Villejo, which were defended by small infantry detachments. Other forces were stationed at la Piedad (1st & 2d Mexico Activos and Guanajunto Battalions), the Insurgente bridge (Gen. Arguelles : Invalidos and Lagos Battalion) and in the rear of these (Gen. Ramirez with 2d Ligero and various pickets) before withdrawing to the Citadel.
Finally they were inside the city and setting up their artillery. Although Santa Anna’s troops still outnumbered Scott’s 2 to 1, Mexican government officials pleaded with Santa Anna to surrender and spare the city. Santa Anna and his men departed that night. Just before dawn on September 14, Mexico City surrendered.
Santa Anna abdicated, but months passed before any Mexican government was willing to negotiate. Polk insisted that the war resume, but Scott ignored the order. Finally, on February 2, 1848, U.S. negotiator Nicholas Trist concluded the Treaty of Guadalupe Hidalgo. Mexico ceded Texas with the Rio Grande boundary, New Mexico (including Arizona, Colorado, Utah, and Nevada), and upper California (including San Diego) to the United States. The U.S. government assumed $3 million in unpaid private U.S. claims against Mexico and paid Mexico an additional $15 million. For a relatively small cost (13,271 deaths, but only 1,721 were killed in battle or died of wounds), the United States greatly expanded its continental area. The debate over the territorial gains so intensified debate over slavery, however, that it hastened the coming of the American Civil War.
Bauer, Jack. The Mexican War, 1846-1848. New York: Macmillan, 1974.
Eisenhower, John S. D. So Far from God: The U.S. War with Mexico, 1846-1848. New
York: Random House, 1989.
Singletary, Otis. The Mexican War. Chicago: University of Chicago Press, 1960.