The Mexican-American War: America’s War for Real Estate

Democrat James A. Polk of Tennessee became president right after John Tyler had annexed Texas into the Union in 1845. Polk was immediately faced with two boundary disputes. One was with Mexico, which felt that the U.S. annexation was illegal, and that there had been a tacit understanding that an act of annexation would be a pretext for war. The other was with the British Empire over setting the northern border of the Oregon Country. The second dispute he was able to resolve with diplomacy. The first dispute led to war.

Texans insisted that their southern border was the Rio Grande. Mexico was equally insistent that it was further north, at the Rio Neuces. The U.S. stationed troops in this disputed area of Texas and waited for an armed Mexican response to provide an excuse for going to war. Mexican soldiers obliged by ambushing a U.S. scouting party, allowing Polk to send a message to Congress claiming the Mexicans had started a war.

Article continues after this newspaper image from the May 16, 1846, issue of the Easton Gazette (Easton, Maryland)

The resulting Mexican-American War had three main theaters. In the first, General Zachary Taylor—"Old Rough and Ready" to his men—invaded northern Mexico and won victories against a succession of Mexican generals. He defeated General Arista at the battle of Resaca de la Palma, General Ampudia at the battle of Monterrey and General Santa Anna (who had used the earlier defeats to return from exile and make himself the ruler of Mexico again) at the battle of Buena Vista.

The war's second theater of operations was California. American settlers in California did not wait for official news of the war's start to rebel. John C. Fremont and his armed party, who had been heading for Oregon, reversed course and started the "Bear Flag Rebellion" in California. Forces under Fremont, Robert F. Stockton and John Drake Sloat quickly conquered northern California and Stockton then sailed south and captured Los Angeles. The Californios, as the Mexican settlers were known, successfully fought back and recaptured Los Angeles. This was how things stood when Stephen Kearny and his men arrived from Missouri, via Santa Fe. Kearny's initial battle was a defeat and his troops were besieged by the victorious Mexicans. He sent to San Diego for help, which arrived in time to rescue his forces. Stockton and Kearny marched north from San Diego to Los Angeles, joined with Fremont's forces and defeated the Californios in several battles, retaking Los Angeles and bringing the armed struggle in California to an end.

In the war's third theater, General Winfield Scott—whose nickname was "Old Fuss and Feathers"—led an invasion of southern Mexico at Veracruz that ultimately led to the conquest of Mexico City. His amphibious landing outside Veracruz was successful, as was his 12-day siege of the city. He then led his troops toward Mexico City, on the way defeating Santa Anna at Cerro Gordo. The large city of Puebla surrendered to him without fighting, opening up the way to Mexico City and ultimate victory for the U.S.

The Mexican-American War had several important impacts on American history. The treaty signed in February of 1848 ceded to the U.S. lands that later became the states of California, Nevada, Utah, and New Mexico as well as most of Arizona and parts of Colorado and Wyoming. The brilliant performance of several West Point graduates during the war quieted the talk in Congress about cutting off the Military Academy's funding. Those officers, who included Ulysses S. Grant, Robert E. Lee and Thomas (later "Stonewall") Jackson, would become the leaders of both sides of the U.S. Civil War. Both Taylor and Scott would run for the presidency as Whigs, with only Taylor winning. Fremont would unsuccessfully run for that office as well, as the first candidate of the new Republican Party.

The arguments in Congress about whether or not to extend slavery to territories won in the Mexican-American War led directly to the Compromise of 1850. This political compromise managed to delay—but ultimately could not prevent—the American Civil War.

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