The War with Mexico and the Treaty of Guadalupe Hidalgo


By Allen GuelzoPrinceton University

There was no question about the enthusiasm Americans displayed for the war, and there was also no question about the dread and resentment of the Mexicans at American claims on Texas. The principal American field force—the principal one of what would be four major field armies the United States put into the Mexican War—would be Zachary Taylor’s, now reinforced up to 3,000 regulars and several thousand ill-disciplined volunteers.

Canon at a battlefield
The American army battered its way through Mexico, winning over it in a clean sweep. (Image: Danita Delimont/Shutterstock)

Conquering Monterey, Nuevo León

By September 19, Taylor had closed in on Monterey, and from September 21 to September 24 American infantry battled their way into the city, fighting across street barricades, dragging their artillery by hand ropes into the streets to blast openings in the Mexican defenses, and lobbing fat mortar shells onto the city plaza.

After losing 120 soldiers, Taylor was relieved when the battered Mexican garrison put out the white flag, and asked on what terms he would permit their surrender. Taylor’s force was too exhausted to demand very much, and so the Mexicans were allowed to evacuate Monterey without surrendering their weapons or their pride. It was, however, the first great victory of the war, the first victory Americans had on foreign soil since the War of 1812.

Return (and Retreat) of Santa Anna

The invasion of Nuevo León set off a flurry of panic in Mexico City. Without offering any particular political guarantees, the American Navy allowed Santa Anna to slip back into Mexico. Instead of promoting peace negotiations, however, this one-time dictator offered his services to the new acting Mexican government, and was given overall command of the Mexican army.

Santa Anna had criticized the stand the Mexican army had made at Monterey as a useless waste of Mexican forces, and his effort to relieve the Monterey garrison, once Taylor showed up there, was fatally delayed by suspicious and uncooperative governors in Durango, Coahuila, and Zacatecas. They believed that Santa Anna was only looking for an opportunity to reinstall himself as dictator.

Santa Anna managed to coax the strength of the Mexican army of the north up to 21,000 cavalry and infantry plus 12 cannon. At the end of January 1847, he moved off to the north to confront Zachary Taylor. On February 22, 1847, the two armies clashed. Wave after wave of Mexican attackers were broken by Taylor’s artillery, and after 36 hours of fighting, Santa Anna called for a retreat.

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Series of American Triumph

Furthermore, President James K. Polk ordered a field colonel, Stephen W. Carney, and some 1,500 men to march overland from Fort Leavenworth in modern-day Kansas to Santa Fe in the province of New Mexico. By August, Carney had captured Santa Fe without a shot.

American settlers in California had obligingly imitated the example of the Texans, staged an uprising against Mexican rule, and proclaimed a republic under a flag with the unusual figure for a flag of a bear. Hence, it was known as the “Bear Flag Republic”. Together, the American settlers, the American troops, and the American sailors defeated the Mexican governor of California and his tiny army at the Battle of San Gabrielle River on January 8, 1847; California fell under American occupation.

Meanwhile, the Missouri volunteers that Carney had left behind in Santa Fe under Donovan went on their own joy ride through New Mexico, capturing El Paso on December 26, 1846. However, the greatest and most daring feat of American arms occurred on the other side of Mexico two weeks after the victory at Buena Vista.

General Winfield Scott

General Winfield Scott landed a major invasion force of 14,000 regulars and volunteers on Mexico’s gulf coast at Vera Cruz.

statue of General Winfield Scott
General Winfield Scott led a series of triumphs in different provinces and states of Mexico. (Image: Bill Perry/Shutterstock)

Since the United States Army had no experience in combining operations between army and navy, Scott’s success in shipping his men on 200 ships, disembarking them under the fire of Mexican coast artillery, and then pounding Vera Cruz into surrender under a hail of American artillery, ranks as one of the great military wonders of the day.

The Fall of Mexico City

Scott’s real objective was the Mexican capital, Mexico City. Santa Anna hardly moved his army south from its defeated Buena Vista to oppose Scott’s march inland. It is also said that at El Gordo on April 18, Santa Anna vainly tried to block Scott’s path, only to be outflanked, overrun, and brought within a whisker of being captured personally by an onrushing brigade of Illinois volunteers.

In August, Scott brushed aside another attempt by the Mexicans to obstruct his march at Contreras, and by late August, he was on the outskirts of Mexico City.

In a series of hammer-like assaults on the outer rings of Mexico City’s defenses, the attack on the convent at Churubusco on August 20, then the foundry at Molino del Rey on September 8, then Chapultepec Castle, defended by the Mexican military academy’s cadets—Los Niños—on September 13, and then finally the attack on the San Cosme Gate. At each stage like this, Scott battered his way into Mexico City, and Santa Anna abandoned the useless struggle.

The Treaty of Guadalupe Hidalgo

With the fall of Mexico City, the war was effectively over. It ended officially with the Treaty of Guadalupe Hidalgo in February of 1848, a treaty whose terms sowed seeds of bitterness that still taint Mexican/American relations.

Mexico was forced to cede two-fifths of its territory, and that included all of the modern-day states of the United States of California, New Mexico, parts of present-day Utah, Nevada, and Colorado. Of course, the Mexican government also had to agree to recognize the Rio Grande River as the true boundary of Texas. Mexico also agreed, on top of all of this, to pay $15 million to settle all Mexican claims and debts to the United States.

Common Questions about War with Mexico and the Treaty of Guadalupe Hidalgo

Q: What was the first major victory of the Americans on foreign soil after the war of 1812?

Zachary Taylor’s field force occupying Monterey was the first great victory of the Mexican war, and the first victory Americans had on foreign soil since the War of 1812.

Q: Who contributed toward capturing Mexico City?

In a series of hammer-like assaults on the outer rings of Mexico City’s defenses, General Winfield Scott battered his way into Mexico City, significantly contributing to its capture.

Q: How did the Mexican war end?

With the fall of Mexico City, the war was effectively over. It ended officially with the Treaty of Guadalupe Hidalgo in February of 1848.

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