Mexican War Ends in U.S. Victory in 1848

Winfield Scott entering Plaza de la Constitución after the Fall of Mexico City

Polk won the presidency in 1844 on a platform embracing the popular concept of “manifest destiny,” that the U.S. had the duty to expand over the continent.

On this day in history, May 19:

Mexico ratified the Treaty of Guadalupe Hidalgo in 1848, officially ending the Mexican War and ceding 500,000 square miles of land to the United States for $18 million. The treaty also stretched the Texas border to the Rio Grande.

The Mexican War was caused by a border dispute after the U.S. annexed Texas in 1845. Mexico believed the southern border of Texas was the Nueces River, while the U.S. claimed it was the Rio Grande. Another major factor was the American goal of acquiring California, coveted by France and Britain.

A secret mission by John Slidell to negotiate the dispute and purchase New Mexico and California for $30 million was aborted when Mexico refused to receive him. President Polk, successful in obtaining Oregon from Britain, continued to make offers, which the Mexican president rejected.

Angered by the U.S. annexation of Texas and attempts to make the Rio Grande the border, Mexico declared a state of “defensive war” on April 23, 1846. Polk sent a 70-man patrol under General Zachary Taylor to occupy the disputed land. Some 2,000 Mexican troops crossed the river and attacked Taylor’s troops.

U.S. Declares War On Mexico

When word of the skirmish reached Washington, Polk — stating that “Mexico has passed the boundary of the United States, has invaded our territory, and shed American blood upon American soil” — asked Congress to approve a declaration of war, which it did on May 13. Mexico officially declared war on July 7.

The fighting began on May 8, and Taylor’s 2,400 troops won the battle of Palo Alto. In the battle of Resaca de la Palma the next day, the two sides engaged in fierce hand to hand combat. The U.S. cavalry captured the enemy artillery, causing the Mexicans to retreat.

Ordered to invade Mexico, Taylor moved southward and captured Monterrey in September and Saltillo in November. U.S. troops also easily occupied Santa Fe and began an overland march to California.

U.S. Wins California

In June 1846, General Stephen Kearny marched to New Mexico with 1,600 soldiers, who he then led across New Mexico, Arizona and the Sonoran Desert, reaching California on December 6. He fought a battle with Californio lancers at the battle of San Pasqual.

Then, the Americans won the battle of La Mesa, and the last significant body of Californios surrendered to U.S. forces, marking the end of armed resistance in California.

The Treaty of Cahuenga was signed on January 13, 1847. Captain John C. Fremont accepted the final surrender of the pro-Mexico resisters, ending 25 years of Mexican rule.

U.S. Captures Mexico City

Taylor defeated a large Mexican force under General Antonio Lopez de Santa Anna at the battle of Buena Vista in February 1847. While Polk and General Winfield Scott made plans to capture Mexico City, Santa Anna, now president, rebuilt his army and prepared to attack Taylor’s forces at Saltillo.

Helped by an intercepted letter containing Santa Anna’s plans, Taylor withstood the assault. As Santa Anna retreated to the capital, Scott followed Polk’s orders and moved his army by sea to Veracruz and captured the city, from where the march inland to Mexico City began.

Scott met resistance at Cerro Gordo and Contreras, but routed the Mexican army and entered the capital of Mexico City uncontested with about 6,500 troops on September 14. The Mexicans suffered more than 1,000 casualties and 3,000 were taken prisoner.

Treaty of Guadalupe Hidalgo

Under the Treaty of Guadalupe Hidalgo, signed on February 2, approved by the U.S. Senate by a 38-14 vote on March 10, and confirmed by both sides on May 30, 1848, the U.S. gained control of Texas and was ceded the present-day states of California, Nevada, Utah, and parts of Colorado, Arizona, New Mexico and Wyoming.

The boundary between the two countries was to follow the Rio Grande from its mouth to the New Mexico line, run west to the Gila River, follow the Gila to the Colorado River, and then the boundary between Upper California and Lower California to the Pacific.

Mexico received $18,250,000, much less than the amount the United States had attempted to offer for the land before the outbreak of hostilities.

Legacy of Mexican War

Due to the war, which resulted in about 13,000 American deaths, Polk greatly expanded the powers of the president as commander in chief. Taylor became a national hero and won the 1848 presidential election. Scott was the Whigs’ presidential nominee in 1852, but lost.

The war heightened tensions over the slavery extension issue, supposedly settled by the Missouri Compromise. A series of postwar measures granted slavery in California, abolished it in Washington, and created the Fugitive Slave Law, hastening the Civil War.

Many military leaders of the Civil War, including Ulysses Grant, Robert E. Lee, P.G.T. Beauregard, Thomas “Stonewall” Jackson, George McClellan, Ambrose Burnside, James Longstreet, George Meade and future Confederate President Jefferson Davis, gained combat experience in the Mexican War.

Civil Disobedience

The Mexican War was opposed by many Americans, particularly the Whig Party, anti-slavery groups, and author Henry David Thoreau, who was jailed for refusing to pay a tax to support it. His essay “Civil Disobedience” explained the principle in 1849.

He argued that people should not permit governments to overrule their consciences and that it was disgraceful to be associated with the U.S. government due to its sanction of slavery, which was immoral and wrong. “This people must cease to hold slaves,” he wrote, “and to make war on Mexico.”

And Grant wrote that he was bitterly opposed to the war and regarded it as “one of the most unjust ever waged by a stronger against a weaker nation. It was an instance of a republic following the bad example of European monarchies, in not considering justice in their desire to acquire additional territory.”


  1. Bauer, K. Jack. The Mexican War. 1974.
  2. Ruiz, R.E. The Mexican War: Was It Manifest Destiny? 1963.