Mexican-American War 101: An Overview

Zachary Taylor during the Mexican-American War
23rd February 1847: American army general Zachary Taylor (1784 - 1850), directing his troops at the Battle of Buena Vista in Northern Mexico during the Mexican-American war. Hulton Archive / Stringer/ Hulton Archive/ Getty Images

The Mexican-American War was a conflict that occurred as the result of Mexican resentment over the US annexation of Texas and a border dispute. Fought between 1846 and 1848, the majority of the significant battles took place between April 1846 and September 1847. The war was fought primarily in northeastern and central Mexico and resulted in a decisive American victory. As a result of the conflict, Mexico was forced to cede its northern and western provinces, which today comprise a significant portion of the western United States. The Mexican-American War represents the only major military dispute between the two nations


The causes of the Mexican-American War can be traced back to Texas winning its independence from Mexico in 1836. At the end of the Texas Revolution following the Battle of San Jacinto, Mexico refused to acknowledge the new Republic of Texas, but was prevented from taking military action due to the United States, Great Britain, and France conferring diplomatic recognition. For the next nine years, many in Texas favored joining the United States, however Washington did not take action due to fears of increasing sectional conflict and angering the Mexicans.

Portrait of James K. Polk
President James K. Polk. Public Domain

Following the election of the pro-annexation candidate, James K. Polk in 1845, Texas was admitted to the Union. Shortly thereafter, a dispute began with Mexico over the southern border of Texas. This centered around whether the border was located along the Rio Grande or further north along the Nueces River. Both sides sent troops to the area and in an effort to lower tensions, Polk dispatched John Slidell to Mexico to begin talks regarding the United States buying territory from the Mexicans.

Commencing negotiations, he offered up to $30 million in exchange for accepting the border at the Rio Grande as well as the territories of Santa Fe de Nuevo Mexico and Alta California. These attempts failed as the Mexican government was unwilling to sell. In March 1846, Polk directed Brigadier General Zachary Taylor to advance his army into the disputed territory and establish a position along the Rio Grande.

General Zachary Taylor. Photograph Source: Public Domain

This decision was a response to new Mexican President Mariano Paredes declaring in his inaugural address that he sought to uphold Mexican territorial integrity as far north as the Sabine River, including all of Texas. Reaching the river, Taylor established Fort Texas and withdrew towards his supply base at Point Isabel. On April 25, 1846, a US cavalry patrol, led by Captain Seth Thornton, was attacked by Mexican troops. Following the “Thornton Affair,” Polk asked Congress for a declaration of war, which was issued on May 13.

Taylor's Campaign in Northeastern Mexico

Following the Thornton Affair, General Mariano Arista ordered Mexican forces to open fire on Fort Texas and lay siege. Responding, Taylor began moving his 2,400-man army from Point Isabel to relieve Fort Texas. On On May 8, 1846, he was intercepted at Palo Alto by 3,400 Mexicans commanded by Arista.

Battle of Resaca de la Palma. Photograph Source: Public Domain

In the battle that ensued Taylor made effective use of his light artillery and forced the Mexicans to retreat from the field. Pressing on, the Americans encountered Arista's army again the next day. In the resulting fight at Resaca de la Palma, with Taylor’s men routed the Mexicans and drove them back across the Rio Grande. Having cleared the road to Fort Texas, the Americans were able to lift the siege.

As reinforcements arrived through the summer, Taylor planned for a campaign in northeastern Mexico. Advancing up the Rio Grande to Camargo, Taylor then turned south with the goal of capturing Monterrey. Battling hot, dry conditions, the American army pushed south and arrived outside of city in September. Though the garrison, led by Lieutenant General Pedro de Ampudia, mounted a tenacious defense, Taylor captured the city after heavy fighting.

American troops fighting in the street of Monterrey
U.S. Army troops attack through the streets of Monterrey, 1846. Public Domain 

When the battle ended, Taylor offered the Mexicans a two month truce in exchange for the city. This move angered Polk who began to strip Taylor’s army of men for use in invading central Mexico. Taylor’s campaign ended in February 1847, when his 4,000 men won a stunning victory over 20,000 Mexicans at the Battle of Buena Vista.

War in the West

In mid-1846, Brigadier General Stephen Kearny was dispatched west with 1,700 men to capture Santa Fe and California. Meanwhile, US naval forces, commanded by Commodore Robert Stockton, descended on the coast of California. With the aid of American settlers and Captain John C. Frémont and 60 men of the US Army who had been en route to Oregon, they swiftly captured the towns along the coast.

In late 1846, they aided Kearny’s exhausted troops as they emerged from the desert and together forced the final surrender of Mexican forces in California. Fighting was ended in the region by the Treaty of Cahuenga in January 1847.

Landing at Veracruz, March 1947. Public Domain

Scott's March to Mexico City

On March 9, 1847, Major General Winfield Scott landed 12,000 men outside of Veracruz. After a brief siege, he captured the city on March 29. Moving inland, he began a brilliantly conducted campaign that saw his army advance deep into enemy territory and routinely defeat larger forces. The campaign opened when Scott's army defeated a larger Mexican army at Cerro Gordo on April 18. As Scott’s army neared Mexico City, they fought successful engagements at Contreras, Churubusco, and Molino del Rey. On September 13, 1847, Scott launched an attack on Mexico City itself, assaulting Chapultepec Castle and capturing the gates of the city. Following the occupation of Mexico City, the fighting effectively ended.

Battle of Chapultepec. Photograph Source: Public Domain

Aftermath & Casualties

The war ended on February 2, 1848, with the signing of the Treaty of Guadalupe Hidalgo. This treaty ceded to the United States the land that now comprises the states of California, Utah, and Nevada, as well as parts of Arizona, New Mexico, Wyoming, and Colorado. Mexico also renounced all rights to Texas. During the war 1,773 Americans were killed in action and 4,152 were wounded. Mexican casualty reports are incomplete, but it estimated that approximately 25,000 were killed or wounded between 1846-1848.

Notable Figures:

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Your Citation
Hickman, Kennedy. "Mexican-American War 101: An Overview." ThoughtCo, Apr. 5, 2023, Hickman, Kennedy. (2023, April 5). Mexican-American War 101: An Overview. Retrieved from Hickman, Kennedy. "Mexican-American War 101: An Overview." ThoughtCo. (accessed June 8, 2023).