Mexican-American War Timeline

Mexican cavalry ambushed an American patrol under Captain Seth Thornton north of the Rio Grande, killing or capturing dozens of soldiers. Polk cited the incident as proof that Mexico had 'shed American blood upon American soil' and used it to justify a declaration of war.

Image source: Thornton Affair

Mexican artillery bombarded the American fortification on the Rio Grande for several days. The siege ended when Taylor's relief force won victories at Palo Alto and Resaca de la Palma, forcing the Mexicans to withdraw across the river.

Image source: Siege of Fort Texas

General Zachary Taylor's army defeated a larger Mexican force near modern Brownsville, Texas, using superior artillery, including new flying grapeshot tactics. It was the first major battle of the war.

Image source: Battle of Palo Alto

Taylor's forces routed the retreating Mexican army in dense brushland near the Rio Grande, capturing General Rómulo Díaz de la Vega and numerous prisoners. The victory secured American control of the disputed territory.

Image source: Battle of Resaca de la Palma

Taylor's army captured the heavily fortified city of Monterrey after brutal urban fighting. Taylor granted the Mexican garrison an eight-week armistice, drawing criticism from President Polk, who wanted unconditional terms.

Image source: Battle of Monterrey

General Stephen Kearny's exhausted dragoons clashed with Californio lancers under Andrés Pico near San Diego. The bloody engagement ended inconclusively, but American reinforcements soon secured the region.

Image source: Battle of San Pasqual

Zachary Taylor's outnumbered army repelled Santa Anna's attack near Saltillo in fierce mountain fighting. The victory made Taylor a national hero and propelled him to the presidency in 1848.

Image source: Battle of Buena Vista

Scott's army outflanked Santa Anna's entrenched positions at Cerro Gordo, routing the Mexican army and capturing thousands of prisoners. Captain Robert E. Lee's reconnaissance played a key role in the flanking maneuver.

Image source: Battle of Cerro Gordo

In two days of intense fighting outside Mexico City, Scott's forces crushed Mexican defenses at Contreras and Churubusco, inflicting heavy casualties. The victories brought the American army within reach of the capital.

Image source: Battle of Churubusco

American troops stormed the fortress of Chapultepec, defended in part by young military cadets known as Los Niños Héroes, several of whom died defending the castle. The fall of Chapultepec left Mexico City exposed.

Image source: Battle of Chapultepec

American settlers in Sonoma seized control of northern California and raised the Bear Flag, declaring the California Republic. Within weeks, U.S. naval forces under Commodore John D. Sloat claimed California for the United States.

Image source: California Republic

Brigadier General Stephen W. Kearny led the Army of the West into New Mexico, taking Santa Fe peacefully as Governor Manuel Armijo declined to resist. Kearny established a territorial government before continuing toward California.

Image source: Stephen W. Kearny

General Winfield Scott executed the largest American amphibious operation to date, landing 12,000 troops south of Veracruz. After a three-week siege and bombardment, the city surrendered, opening the road to Mexico City.

Image source: Siege of Veracruz

Scott's army entered the major city of Puebla largely unopposed and rested there for months while awaiting reinforcements. The pause allowed Scott to rebuild his strength before the final push to the capital.

Image source: Puebla

Winfield Scott's army marched into the Mexican capital, becoming the first foreign army to occupy Mexico City. Marines have since commemorated the capture in the opening line of the 'Marines' Hymn.'

Just days before the peace treaty was signed, gold was discovered at Sutter's Mill in newly acquired California. The Gold Rush drew hundreds of thousands of settlers westward and accelerated California's path to statehood.

Image source: California Gold Rush

Nicholas Trist, acting despite Polk's order to recall him, negotiated a peace treaty with Mexico. The treaty set the Rio Grande as the Texas border and ceded vast territories including California and New Mexico to the United States for $15 million.

The Senate ratified the Treaty of Guadalupe Hidalgo by a vote of 38 to 14 after modifying some articles. Mexico ratified it in May, formally ending the war and confirming the massive territorial transfer.

Image source: Treaty of Guadalupe Hidalgo

War hero General Zachary Taylor won the presidency as the Whig candidate, defeating Lewis Cass. Ironically, Taylor had opposed Polk's expansionist ambitions even while leading armies during the war.

Image source: 1848 United States presidential election

As part of the Compromise of 1850, California entered the Union as a free state, bypassing territorial status thanks to its explosive growth during the Gold Rush. The compromise temporarily eased sectional tensions inflamed by the war's territorial gains.

Image source: Compromise of 1850

The United States purchased a strip of land in present-day southern Arizona and New Mexico from Mexico for $10 million, finalizing the continental boundaries sought during the Mexican-American War era and enabling a southern transcontinental railroad route.

Image source: Gadsden Purchase