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The Mexican–American War, also known in the United States as the Mexican War, and in Mexico as the United States intervention in Mexico, was an invasion of Mexico by the United States Army from 1846 to 1848.
- April 25, 1846 – February 2, 1848, (1 year, 9 months, 1 week and 1 day)
- Overview
- “American blood on American soil”: Polk and the prelude to war
- Spot Resolutions and Civil Disobedience: American opposition to the war
The Mexican-American War was a conflict between the United States and Mexico, fought from April 1846 to February 1848. Won by the Americans and damned by its contemporary critics as expansionist, it resulted in the U.S. gaining more than 500,000 square miles (1,300,000 square km) of Mexican territory extending westward from the Rio Grande to the Pacific Ocean. It stemmed from the annexation of the Republic of Texas by the U.S. in 1845 and from a dispute over whether Texas ended at the Nueces River (the Mexican claim) or the Rio Grande (the U.S. claim).
What did the Mexican-American War have to do with Manifest Destiny?
The concept of Manifest Destiny held that the United States had the providential right to expand to the Pacific Ocean. In 1845 the U.S. annexed the Republic of Texas, which had won de facto independence from Mexico in the Texas Revolution (1835–36). When U.S. diplomatic efforts to establish agreement on the Texas-Mexico border and to purchase Mexico’s California and New Mexico territories failed, expansionist U.S. Pres. James K. Polk found a rationale to justify an attempt to take that land by force when U.S. and Mexican troops skirmished north of the Rio Grande on April 25, 1846.
Manifest Destiny
Read more about Manifest Destiny.
James K. Polk
Mexico severed relations with the United States in March 1845, shortly after the U.S. annexation of Texas. In September U.S. Pres. James K. Polk sent John Slidell on a secret mission to Mexico City to negotiate the disputed Texas border, settle U.S. claims against Mexico, and purchase New Mexico and California for up to $30 million. Mexican Pres. José Joaquín Herrera, aware in advance of Slidell’s intention of dismembering the country, refused to receive him. When Polk learned of the snub, he ordered troops under Gen. Zachary Taylor to occupy the disputed area between the Nueces and the Rio Grande (January 1846).
On May 9, 1846, Polk began to prepare a war message to Congress, justifying hostilities on the grounds of Mexican refusal to pay U.S. claims and refusal to negotiate with Slidell. That evening he received word that Mexican troops had crossed the Rio Grande on April 25 and attacked Taylor’s troops, killing or injuring 16 of them. In his quickly revised war message—delivered to Congress on May 11—Polk claimed that Mexico had “invaded our territory and shed American blood on American soil.”
Congress overwhelmingly approved a declaration of war on May 13, but the United States entered the war divided. Democrats, especially those in the Southwest, strongly favoured the conflict. Most Whigs viewed Polk’s motives as conscienceless land grabbing. Indeed, from the outset, Whigs in both the Senate and the House challenged the veracity of Polk’s assertion that the initial conflict between U.S. and Mexican forces had taken place in U.S. territory. Further, legislators were at odds over whether Polk had the right to unilaterally declare that a state of war existed. Principally at issue was where the encounter had actually taken place and the willingness of Americans to acknowledge the Mexican contention that the Nueces River formed the border between the two countries. Active Whig opposition not only to the legitimacy of Polk’s claim but also to the war itself continued well into the conflict. In December 1846 Polk accused his Whig doubters of treason. In January 1847 the by-then Whig-controlled House voted 85 to 81 to censure Polk for having “unnecessarily and unconstitutionally” initiated war with Mexico.
Britannica Quiz
A History of War
Among the most-aggressive challenges to the legitimacy of Polk’s casus belli was that offered by future president Abraham Lincoln, then a first-term member of the House of Representatives from Illinois. In December 1847 Lincoln introduced eight “Spot Resolutions,” which placed the analysis of Polk’s claim in a carefully delineated historical context that sought to
obtain a full knowledge of all the facts which go to establish whether the particular spot of soil on which the blood of our citizens was so shed was, or was not, our own soil at that time.
Ultimately, the House did not act on Lincoln’s resolutions, and Polk remained steadfast in his claim that the conflict was a just war.
- The Editors of Encyclopaedia Britannica
Nov 9, 2009 · The Mexican-American War of 1846 to 1848 marked the first U.S. armed conflict chiefly fought on foreign soil.
May 14, 2020 · A Brief Overview of the Mexican-American War 1846-1848. May 14, 2020 • Updated November 29, 2023. Two long years had passed after the initial shots were fired, sparking the Mexican American War in 1846.
Nov 9, 2009 · The Treaty of Guadalupe Hidalgo, signed on February 2, 1848, ended the Mexican-American War in favor of the United States.
- 4 min
Sep 20, 2022 · 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.
This timeline describes significant events during the Mexican-American War, which was fought between Mexico and the United States from 1846 to 1848. The war stemmed from the United States’ annexation of Texas in 1845 and from a dispute over whether Texas ended at the Nueces River (Mexican claim) or the Rio Grande (U.S. claim).
