Mexican–American War

Mexican–American War. The Mexican–American War was an armed conflict between the United States and Mexico from 1846 to 1848. It followed the 1845 American annexation of the Republic of Texas, which Mexico still considered its territory, and was driven by American expansionist ideals, often termed Manifest Destiny. The war concluded with the decisive defeat of Mexican forces, the occupation of Mexico City by the U.S. Army, and a treaty that dramatically altered the map of North America.

Background and causes

The primary cause was the annexation of Texas by the United States in 1845, a region Mexico had never formally recognized as independent following the Texas Revolution. Under President James K. Polk, the U.S. government sought to acquire Mexican territories, including Alta California and New Mexico, through purchase, but the offer was rejected by the government in Mexico City. A longstanding border dispute existed, with the U.S. claiming the Rio Grande as the boundary per the Treaty of Velasco, while Mexico insisted the border was the Nueces River farther north. Polk’s deployment of troops under General Zachary Taylor into this disputed territory was a deliberate provocation that escalated tensions significantly.

Outbreak of war

Hostilities commenced on April 25, 1846, when a Mexican cavalry detachment attacked a U.S. patrol north of the Rio Grande near Fort Texas in the disputed zone, an event known as the Thornton Affair. Upon receiving news of the clash, President James K. Polk declared to the U.S. Congress that Mexico had "invaded our territory and shed American blood upon the American soil." The U.S. Congress subsequently passed a declaration of war on May 13, 1846. Mexico, under President Mariano Paredes y Arrillaga, issued its own declaration, framing the conflict as a defensive war against an aggressive invasion by the United States.

Major campaigns and battles

The war was fought across multiple fronts. In northern Mexico, General Zachary Taylor won early victories at the Battle of Palo Alto and the Battle of Resaca de la Palma, then captured Monterrey after a fierce battle. His triumph over a larger Mexican force led by Antonio López de Santa Anna at the Battle of Buena Vista in February 1847 secured the northern theater. Concurrently, Colonel Stephen W. Kearny led the Army of the West to capture Santa Fe and proceeded to California, where U.S. naval forces under Commodore John D. Sloat and the California Battalion led by John C. Frémont had already initiated the Conquest of California. The decisive campaign was led by General Winfield Scott, who executed a major amphibious landing at Veracruz and then fought a brilliant inland campaign, culminating in the capture of Mexico City following battles at Cerro Gordo, Contreras, Churubusco, and the final assault on Chapultepec Castle.

Treaty of Guadalupe Hidalgo and aftermath

The fall of Mexico City forced the Mexican government to negotiate. The war was formally ended by the Treaty of Guadalupe Hidalgo, signed on February 2, 1848, in the Villa de Guadalupe Hidalgo. The treaty required Mexico to cede a vast territory, known as the Mexican Cession, which included present-day California, Nevada, Utah, most of Arizona, and parts of New Mexico, Colorado, and Wyoming. The United States agreed to pay Mexico $15 million and assume up to $3.25 million in debts owed by Mexico to American citizens. The treaty also established the Rio Grande as the border for Texas and promised to protect the property and civil rights of Mexicans remaining in the ceded territories, promises that were often not upheld in the following decades.

Consequences and legacy

The war had profound and lasting consequences for both nations. For the United States, it realized the goals of Manifest Destiny, adding over 500,000 square miles of territory and providing immense natural resources, but it also intensified the national debate over the expansion of slavery, leading directly to the Compromise of 1850 and increasing sectional strife that culminated in the American Civil War. For Mexico, the loss of half its national territory was a catastrophic and humiliating defeat that fueled political instability and a deep-seated resentment toward the United States. The war established several future American Civil War generals, including Ulysses S. Grant and Robert E. Lee, and is remembered in Mexico as a defining event of national sovereignty and resistance.

Category:Wars involving the United States Category:Wars involving Mexico Category:1840s conflicts