The Mexican-American War, 1846–1848

War with Mexico, 1846-1848

In 1845, when Texas joined the United States, Mexico insisted the United States had a right only to the territory northeast of the Nueces River. The United States argued in turn that it should have title to all land between the Nueces and the Rio Grande as well.

Expansionistic fervor propelled the United States to war against Mexico in 1846. The United States had long argued that the Rio Grande was the border between Mexico and the United States, and at the end of the Texas war for independence Santa Anna had been pressured to agree. Mexico, however, refused to be bound by Santa Anna’s promises and insisted the border lay farther north, at the Nueces River. To set it at the Rio Grande would, in effect, allow the United States to control land it had never occupied. In Mexico’s eyes, therefore, President Polk violated its sovereign territory when he ordered U.S. troops into the disputed lands in 1846. From the Mexican perspective, it appeared the United States had invaded their nation.

In January 1846, the U.S. force that was ordered to the banks of the Rio Grande to build a fort on the “American” side encountered a Mexican cavalry unit on patrol. Shots rang out, and sixteen U.S. soldiers were killed or wounded. Angrily declaring that Mexico “has invaded our territory and shed American blood upon American soil,” President Polk demanded the United States declare war on Mexico. On May 12, Congress obliged.

The small but vocal antislavery faction decried the decision to go to war, arguing that Polk had deliberately provoked hostilities so the United States could annex more slave territory. Illinois representative Abraham Lincoln and other members of Congress issued the “Spot Resolutions” in which they demanded to know the precise spot on U.S. soil where American blood had been spilled. Many Whigs also denounced the war. Democrats, however, supported Polk’s decision, and volunteers for the army came forward in droves from every part of the country except New England, the seat of abolitionist activity. Enthusiasm for the war was aided by the widely held belief that Mexico was a weak, impoverished country and that the Mexican people, perceived as ignorant, lazy, and controlled by a corrupt Roman Catholic clergy, would be easy to defeat.

A lithograph shows several members of the clergy fleeing the Mexican town of Matamoros on horseback. Each man has a young woman behind him; the horse in the foreground also carries a basket laden with bottles of alcohol. The caption reads “The Mexican Rulers. Migrating from Matamoros with their Treasures.”
Figure 2. Anti-Catholic sentiment played an important role in the Mexican-American War. The American public widely regarded Roman Catholics as cowardly and vice-ridden, like the clergy in this ca. 1846 lithograph who are shown fleeing the Mexican town of Matamoros accompanied by pretty women and baskets full of alcohol. (credit: Library of Congress)

 

U.S. military strategy had three main objectives: 1) Take control of northern Mexico, including New Mexico; 2) seize California; and 3) capture Mexico City. General Zachary Taylor and his Army of the Center were assigned to accomplish the first goal, and with superior weapons they soon captured the Mexican city of Monterrey. Taylor quickly became a hero in the eyes of the American people, and Polk appointed him commander of all U.S. forces.

General Stephen Watts Kearny, commander of the Army of the West, accepted the surrender of Santa Fe, New Mexico, and moved on to take control of California, leaving Colonel Sterling Price in command. Despite Kearny’s assurances that New Mexicans need not fear for their lives or their property, and in fact the region’s residents rose in revolt in January 1847 in an effort to drive the Americans away. Although Price managed to put an end to the rebellion, tensions remained high.

Kearny, meanwhile, arrived in California to find it already in American hands through the joint efforts of California settlers, U.S. naval commander John D. Sloat, and John C. Fremont, a former army captain and son-in-law of Missouri senator Thomas Benton. Sloat, at anchor off the coast of Mazatlan, learned that war had begun and quickly set sail for California. He seized the town of Monterey in July 1846, less than a month after a group of American settlers led by William B. Ide had taken control of Sonoma and declared California a republic. A week after the fall of Monterey, the navy took San Francisco with no resistance. Although some Californios staged a short-lived rebellion in September 1846, many others submitted to the U.S. takeover. Thus Kearny had little to do other than take command of California as its governor.

Leading the Army of the South was General Winfield Scott. Both Taylor and Scott were potential competitors for the presidency, and believing—correctly—that whoever seized Mexico City would become a hero, Polk assigned Scott the campaign to avoid elevating the more popular Taylor, who was affectionately known as “Old Rough and Ready.”

Scott captured Veracruz in March 1847, and moving in a northwesterly direction from there (much as Spanish conquistador Hernán Cortés had done in 1519), he slowly closed in on the capital. Every step of the way was a hard-fought victory, however, and Mexican soldiers and civilians both fought bravely to save their land from the American invaders. Mexico City’s defenders, including young military cadets, fought to the end. According to legend, cadet Juan Escutia’s last act was to save the Mexican flag, and he leapt from the city’s walls with it wrapped around his body. On September 14, 1847, Scott entered Mexico City’s central plaza; the city had fallen. While Polk and other expansionists called for “all Mexico,” the Mexican government and the United States negotiated for peace in 1848, resulting in the Treaty of Guadalupe Hidalgo.

A painting depicts General Winfield Scott on a white horse leading troops into Mexico City’s Plaza de la Constitución as anxious residents of the city look on. One woman peers furtively from behind the curtain of an upstairs window. On the left, a man bends down to pick up a paving stone to throw at the invaders.
Figure 3. General Scott’s Entrance into Mexico (1851), Carl Nebel depicts General Winfield Scott on a white horse entering Mexico City’s Plaza de la Constitución as anxious residents of the city watch. One woman peers furtively from behind the curtain of an upstairs window. On the left, a man bends down to pick up a paving stone to throw at the invaders.

 

The Treaty of Guadalupe Hidalgo, signed in February 1848, was a triumph for American expansionism under which Mexico ceded nearly half its land to the United States. The Mexican Cession, as the conquest of land west of the Rio Grande was called, included the current states of California, New Mexico, Arizona, Nevada, Utah, and portions of Colorado and Wyoming. Mexico also recognized the Rio Grande as the border with the United States. Mexican citizens in the ceded territory were promised U.S. citizenship in the future when the territories they were living in became states. In exchange, the United States agreed to assume $3.35 million worth of Mexican debts owed to U.S. citizens, paid Mexico $15 million for the loss of its land, and promised to guard the residents of the Mexican Cession from Indian raids.

As extensive as the Mexican Cession was, some argued the United States should not be satisfied until it had taken all of Mexico. Many who were opposed to this idea were southerners who, while desiring the annexation of more slave territory, did not want to make Mexico’s large mestizo (people of mixed Indian and European ancestry) population part of the United States. Others did not want to absorb a large group of Roman Catholics. These expansionists could not accept the idea of new U.S. territory filled with mixed-race, Catholic populations.