Mexican-American War (1846 - 1848)

Mexican-American War (1846 - 1848)
Mexican-American War (1846 - 1848)

In a profound national humiliation for Mexico and the biggest land-grab in U.S. history, from April 1846 to February 1848 the United States waged a war of conquest against its southern neighbor that had major repercussions for both nations.

For Mexico, La Guerra de ’47 discredited the leadership of José Antonio López de Santa Ana and his cohort of ruling conservatives, setting the stage for the emergence of a new generation of liberal reformers after 1855. It also created in Mexican national consciousness a combination of resentment, fear, and respect toward its northern neighbor that endured well into the 20th century.

For the United States, the war added 1.3 million square kilometers to the young republic, thus fulfilling the vision of proponents of the notion of Manifest Destiny by spreading U.S. dominion from the Atlantic to the Pacific Oceans. It also sharpened the sectional division between North and South and played a key role in the eruption of the American Civil War 13 years later.

Before the war, most of this vast region was claimed by Mexico but not under its effective dominion. Comprising the northern frontier of the viceroyalty of New Spain and inherited by Mexico after independence in 1821, the region was inhabited by perhaps 75,000 people, some of Spanish descent and perhaps as many native peoples.

The Spanish-speaking population was clustered in two main zones: the Upper Río Grande Valley, centered on Santa Fe (in present-day New Mexico); and further west in the ribbon of missions and settlements hugging the Pacific coast of California from San Diego to San Francisco. The vast bulk of the conquered region was given over to an intricate mosaic of sedentary, semi-sedentary, and nomadic native peoples in the throes of dramatic changes.

The long-term roots of the war lay in the aggressively expansionist ideology of Manifest Destiny, shared by the most prominent U.S. politicians and opinion-makers in the aftermath of the 1803 Louisiana Purchase and the War of 1812 with Britain.

War in Mexico city
War in Mexico city

The war had an important precedent in the Texas War of Independence in 1836, in which a highly militarized and well organized group of Anglo-Americans wrested Texas from Mexico.

After 1836 debates swirled regarding the status of Texas. Most Anglo Texans urged annexation to the Union, as did many white Americans west of the Mississippi and in the Southern slaveholding states.

In 1844 at the prompting of President Tyler, Texas applied for statehood for a second time (it first applied in 1836), an initiative defeated in the Senate by a coalition of Northern non-slave states.

In the presidential elections of 1844, former governor of Tennessee James K. Polk was elected on a platform of reoccupying Oregon territory and annexing Texas.

After Texas became a state in December 1845, Mexico protested by breaking diplomatic relations with Washington. Meanwhile, pressures were mounting in Washington and beyond for the acquisition of New Mexico and California territories.

Rebuffed in its bid to purchase the land, the Polk administration turned to war. Using the pretext of a border conflict between U.S. and Mexican troops in the disputed territory between the Rios Grande and Nueces in southeastern Texas, on May 13, 1846, the U.S. Congress declared war on Mexico.

The war itself, the subject of an expansive literature, was more hard fought than U.S. policy makers had anticipated. In summer 1846 General Stephen W. Kearney’s Army of the West captured Santa Fe before marching west to California, where it linked up with an expedition led by Colonel John C. Frémont.

By early 1847 the two principal zones of Mexican settlement in what later became the U.S. Southwest were in U.S. hands. Meanwhile forces under General Zachary Taylor marched south from the disputed territory in Texas, meeting unexpectedly fierce resistance before taking Monterrey in September 1846.

The third arm of the offensive, the Army of the Occupation led by General Winfield Scott, invaded Mexico on the southern outskirts of the city of Veracruz in March 1847.

Bombarding the walled city for 48 hours with some 6,700 artillery shells, killing hundreds of civilians and reducing much of the city to rubble, Scott’s army moved methodically westward, following the same route as Hernán Cortés 328 years earlier, taking Mexico City on September 13, 1847 after several weeks of fierce fighting that left thousands dead.

By the terms of the February 2, 1848, Treaty of Guadalupe-Hidalgo that formally ended the war, the United States acquired the northern two-fifths of the national territory claimed by Mexico, a region embracing the present-day states of Texas, New Mexico, Arizona, California, Nevada, and parts of Utah and Colorado.

In exchange Mexico received $15 million in cash, plus $3.25 million in U.S. assumption of outstanding claims—about $14 per square kilometer. The treaty also guaranteed full U.S. citizenship of Mexican nationals in the ceded lands, a provision to which the U.S. government did not adhere in the long term.

In subsequent years, the landholding Spanish-descended californios (settlers in California) were stripped of their lands and political rights, while many of the Spanish-speaking peoples of the Southwest, especially in Texas, New Mexico, and Colorado, became second-class citizens and a low-wage labor force in the region’s burgeoning commercial agriculture, ranching, and mining industries.

In the shorter term, the war sharpened the sectional conflict between North and South by reopening the divisive issue of the expansion of slavery into the territories, initiating a chain of events that led directly to the Compromise of 1850, a deeply flawed agreement whose unraveling 11 years later resulted in the Civil War—a war in which many of the most prominent military leaders on both sides were veterans of the Mexican campaigns.