Mexican-American War - Invasion, Conflict, Treaty (2025)

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Also known as: Guerra de 1847, Guerra de Estados Unidos a Mexico, Mexican War

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Last Updated: Article History

When war broke out, former Mexican president and general Antonio López de Santa Anna (the vanquisher of the Texan forces at the Alamo in 1836) contacted Polk. The U.S. president arranged for a ship to take Santa Anna from his exile in Cuba to Mexico for the purpose of working for peace. Instead of acting for peace, however, on his return, Santa Anna took charge of the Mexican forces.

Following its original plan for the war, the United States sent its army from the Rio Grande, under Taylor, to invade the heart of Mexico while a second force, under Col. Stephen Kearny, was to occupy New Mexico and California. Kearny’s campaign into New Mexico and California encountered little resistance, and the residents of both provinces appeared to accept U.S. occupation with a minimum of resentment. Meanwhile, Taylor’s army fought several battles south of the Rio Grande, captured the important city of Monterrey, and defeated a major Mexican force at the Battle of Buena Vista in February 1847. But Taylor showed no enthusiasm for a major invasion of Mexico, and on several occasions he failed to pursue the Mexicans vigorously after defeating them. In disgust, Polk revised his war strategy. He ordered Gen. Winfield Scott to take an army by sea to Veracruz, capture that key seaport, and march inland to Mexico City. Scott took Veracruz in March after a siege of three weeks and began the march to Mexico City. Despite some Mexican resistance, Scott’s campaign was marked by an unbroken series of victories, and he entered Mexico City on September 14, 1847. The fall of the Mexican capital ended the military phase of the conflict.

Ultimately, infection and disease took many more U.S. casualties than combat did. At least 10,000 troops died of illness, whereas some 1,500 were killed in action or died of battle wounds (estimates of the war’s casualties vary). Poor sanitation contributed to the spread of illness, with volunteers—who were less disciplined in their sanitary practices than regular troops were—dying in greater numbers than the regulars. Yellow fever was particularly virulent, but other diseases—such as measles, mumps, and smallpox—took their toll too, especially on troops from rural environments whose immunities were less developed than those of their urban compatriots.

Treaty of Guadalupe Hidalgo and the war’s legacy

Polk had assigned Nicholas Trist, chief clerk in the State Department, to accompany Scott’s forces and to negotiate a peace treaty. But after a long delay in the formation of a new Mexican government capable of negotiations, Polk grew impatient and recalled Trist. Trist, however, disobeyed his instructions and on February 2, 1848, signed the Treaty of Guadalupe Hidalgo. According to the treaty, which was subsequently ratified by both national congresses, Mexico ceded to the United States nearly all the territory now included in the states of New Mexico, Utah, Nevada, Arizona, California, Texas, and western Colorado for $15 million and U.S. assumption of its citizens’ claims against Mexico.

Mexican-American War events

Battle of Palo AltoMay 8, 1846 Battle of MonterreySeptember 20, 1846 - September 24, 1846 Battle of Buena VistaFebruary 22, 1847 - February 23, 1847 Battle of Cerro GordoApril 1847 Battle of ContrerasAugust 19, 1847 - August 20, 1847 Battle of ChapultepecSeptember 12, 1847 - September 14, 1847

Zachary Taylor emerged as a national hero and succeeded Polk as president in 1849. The war reopened the slavery-extension issue, which had been largely dormant since the Missouri Compromise. On August 8, 1846, Rep. David Wilmot of Pennsylvania attempted to add an amendment to a treaty appropriations bill. The Wilmot Proviso—banning slavery from any territory acquired from Mexico—was never passed, but it led to acrimonious debate and contributed greatly to the rising sectional antagonism. The status of slavery in the newly acquired lands was eventually settled by the Compromise of 1850, but only after the nation had come perilously close to civil war. When the Civil War came in 1861, many of the most-noteworthy generals on both sides had profited from their battle experience in the Mexican-American War, including Confederate Generals Robert E. Lee, Thomas (“Stonewall”) Jackson, James Longstreet, George Pickett, Albert Sidney Johnston, Lewis Armistead, and P.G.T. Beauregard, as well as Union Generals Ulysses S. Grant (who later called the Mexican War “one of the most unjust ever waged by a stronger against a weaker nation”), George Gordon Meade, George H. Thomas, and Joseph Hooker.

In Mexico the war discredited the conservatives but left a stunned and despondent country. It also reinforced the worst stereotypes each country held about the other. Normalization of relations after the war proceeded slowly.

The Editors of Encyclopaedia BritannicaThis article was most recently revised and updated by Adam Zeidan.

Mexican-American War - Invasion, Conflict, Treaty (2025)

FAQs

Mexican-American War - Invasion, Conflict, Treaty? ›

According to the treaty, which was subsequently ratified by both national congresses, Mexico ceded to the United States nearly all the territory now included in the states of New Mexico, Utah, Nevada, Arizona, California, Texas, and western Colorado for $15 million and U.S. assumption of its citizens' claims against ...

What was the Treaty in the Mexican-American War? ›

The Treaty of Guadalupe Hidalgo, which brought an official end to the Mexican-American War (1846-48), was signed on February 2, 1848, at Guadalupe Hidalgo, a city to which the Mexican government had fled with the advance of U.S. forces.

What was the Treaty of the Mexican revolution? ›

The Treaty of Ciudad Juárez was a peace treaty signed between the President of Mexico, Porfirio Díaz, and the revolutionary Francisco Madero on May 21, 1911. The treaty put an end to the fighting between forces supporting Madero and those of Díaz and thus concluded the initial phase of the Mexican Revolution.

What Treaty ended the Mexican-American War What were the outcomes? ›

On February 2, 1848, the United States and Mexico signed the treaty of Guadalupe-Hidalgo. In the Treaty, Mexico agreed to surrender all claims to Texas and accept the Rio Grande as the boundary of that state.

What was the Treaty between the U.S. and Mexico border? ›

Treaty of February 2, 1848 (Treaty of Guadalupe Hidalgo)

The Treaty of February 2, 1848 established the United States-Mexico international boundary. The treaty established temporary joint commissions to survey, map, an demarcate with ground landmarks the new United States - Mexico boundary.

What were three major consequences of the Treaty of Guadalupe Hidalgo for Mexico? ›

The Treaty of Guadalupe Hidalgo, signed on February 2, 1848, ended the Mexican War, recognized the annexation of Texas to the United States (consummated nearly three years before), ceded to the United States Upper California (the modern state of California) and nearly all of the present American Southwest between ...

What were two ways the Treaty of Guadalupe Hidalgo was significant? ›

In a standard Mexican-American history, the Treaty is cited not only as transferring territorial control (“we did not cross the border, the border crossed us”) but as guaranteeing the full rights of citizenship for Mexicans in the Untied States, including the right to speak Spanish.

What was the Treaty of 1944 with Mexico? ›

1944 Treaty Overview

Under the 1944 Treaty , Mexico has an obligation to deliver to the United States 1,750,000 acre-feet (AF) of water over a five-year cycle, at an average of 350,000 AF annually for the five-year cycle.

What is the name of the Treaty that ended the Mexican-American War and established the US Mexico border at the Rio Grande adding 500000 square miles to Texas? ›

Treaty of Guadalupe Hidalgo and the war's legacy

Trist, however, disobeyed his instructions and on February 2, 1848, signed the Treaty of Guadalupe Hidalgo.

What was the Mexican War cession? ›

Under the terms of the treaty negotiated by Trist, Mexico ceded to the United States Upper California and New Mexico. This was known as the Mexican Cession and included present-day Arizona and New Mexico and parts of Utah, Nevada, and Colorado (see Article V of the treaty).

Why did the US invade Mexico? ›

On May 12, 1846, the United States Senate voted 40 to 2 to go to war with Mexico. President James K. Polk had accused Mexican troops of having attacked Americans on U.S. soil, north of the Rio Grande. But Mexico claimed this land as its own territory and accused the American military of having invaded.

Why didn't the US take all of Mexico? ›

Idealistic advocates of Manifest Destiny, such as John L. O'Sullivan, had always maintained that the laws of the United States should not be imposed onto people against their will. The annexation of all of Mexico would violate that principle and find controversy by extending US citizenship to millions of Mexicans.

What happened to Mexicans after the Treaty of Guadalupe Hidalgo? ›

For example, the Treaty of Guadalupe Hidalgo granted federal citizenship to thousands of Mexicans who gradually gained full citizenship through the admission of the various states.

What was the Mexican-American War Treaty? ›

The Treaty of Guadalupe Hidalgo officially ended the Mexican–American War (1846–1848).

Why did Mexico sell land to the US? ›

Santa Anna refused to sell a large portion of Mexico, but he needed money to fund an army to put down ongoing rebellions, so on December 30, 1853 he and Gadsden signed a treaty stipulating that the United States would pay $15 million for 45,000 square miles south of the New Mexico territory and assume private American ...

What were the two causes of the Mexican-American War? ›

One of the causes of this war were the continued claims to Texas from both the United States and Mexican governments. Other reasons were claims against the Mexican government by American citizens for damages during the continuous Mexican Revolutions of the period and the U.S. desire to claim California.

What did Mexico agree to in the Treaty? ›

On February 2, 1848, Nicholas Trist and Mexican peace commissioners signed the Treaty of Guadalupe Hidalgo. In the principal articles of the treaty, Mexico ceded Upper California and New Mexico to the United States, and agreed to recognize the Rio Grande as the boundary of Texas.

What is the purpose of the Treaty of Paris? ›

The Treaty of Paris (1898) officially ended the period of Spanish colonization in the Philippines and granted possession of Cuba, Puerto Rico, Guam, and the Philippines to the United States.

What was the Treaty of Guadalupe Hidalgo for kids? ›

The Treaty of Guadalupe Hidalgo formally ended the war. The United States and Mexico signed the agreement on February 2, 1848. The treaty gave the United States more than 500,000 square miles (1,300,000 square kilometers) of Mexican territory—from the Rio Grande west to the Pacific Ocean.

Why did the US want the Mexican Cession? ›

As the Mexican-American War came to an end, gold was discovered in California, causing a massive population surge on the West Coast that ensured continued American sovereignty over the entire West Coast and paved the way for the boundary conflict in the San Juan Islands.

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