Mexican War

Mexican War (1846–1848), the first photographed war, the first U.S. war covered by newspaper correspondents, and the first fought mostly on foreign soil.One of America's most successful conflicts militarily, the Mexican War added vast territories to the national domain. It also, however, provoked anti‐Americanism in Mexico and contributed to the sectional tension that culminated in the Civil War.

Although some historians trace the Mexican War's underlying causes to political instability in Mexico and the bellicosity of Mexico's leaders, most interpret the conflict as an outgrowth of U.S. expansionism (expressed in the popular slogan “Manifest Destiny,” coined in 1845). According to this view, President James Knox Polk was so bent upon acquiring California ports and other Mexican territory, in part to preempt rumored British designs on California, that he provoked war as a pretext for conquest. Other scholars, however, contend that Polk sought a peaceful resolution of outstanding issues and conducted his prewar diplomacy with Mexico in good faith.

In an immediate sense, warfare erupted because of a dispute over the boundary separating Mexico and Texas, exacerbated by Mexico's defaulting in 1844 on payments to satisfy American citizens' claims for losses sustained in Mexico. The U.S. government, after annexing the Republic of Texas in 1845, upheld Texas's claim to the Rio Grande River as its border with Mexico. Mexican authorities neither recognized Texas's independence from Mexico (achieved in 1836) nor its annexation by the United States; they also claimed that Texas extended only to the Nueces River. On 13 January 1846, the Polk administration ordered General Zachary Taylor's “Army of Occupation” to advance through the disputed region to the Rio Grande. On 23 April, Mexican cavalry crossed the Rio Grande and two days later ambushed a scouting party of Taylor's dragoons, killing eleven soldiers, wounding others, and taking sixty‐three prisoners. Polk asked Congress for war on 11 May, asserting that Mexico had “shed American blood upon American soil.” That same day the House of Representatives passed a war bill by a vote of 173–14. The Senate followed suit on 12 May, by a 40–2 margin.

Although the United States entered the war with an army of fewer than seven thousand officers and men (less than one‐third the size of Mexico's establishment), American troops invaded Mexico and repeatedly defeated numerically superior Mexican forces while U.S. naval vessels blockaded Mexican ports. After routing Mexican troops at Palo Alto (8 May) and Resaca de la Palma (9 May), Taylor's army crossed the Rio Grande on 18 May and subsequently conquered much of northern Mexico, including Monterrey, the capital of the state of Nuevo León, which Taylor occupied under an armistice accord with Mexican officials following heavy fighting on 21 and 23 September. Taylor's campaigns culminated in his defeat of Mexican general Antonio López de Santa Anna's army at Buena Vista, on 22–23 February 1847. By then, General Stephen W. Kearny's Army of the West had occupied New Mexico and U.S. naval and ground forces had conquered California. The American military effort climaxed with Winfield Scott's Mexico City campaign. Scott (1786–1866), the U.S. Army's commanding general, captured Veracruz on the Gulf of Mexico in March 1847 after extensive siege operations, and then invaded Mexico's interior, routing Santa Anna's army at Cerro Gordo (17–18 April). Following victories near Mexico City on 20 August and a costly, avoidable action at Molino del Rey (8 September), Scott's forces routed Mexican defenders from Chapultepec Castle on 13 September and the next day occupied Mexico City, evacuated by Santa Anna the previous night.

The Treaty of Guadalupe‐Hidalgo, signed by U.S. negotiator Nicholas P. Trist with Mexican officials on 2 February 1848 and ratified by the U.S. Senate on 10 March, ended the war. It ceded to the United States some 500,000 square miles—including the disputed boundary area and what would become today's states of California, New Mexico, Arizona, Utah, Nevada, and parts of Colorado and Wyoming—in return for $15 million and the U.S. government's assumption of up to $3.25 million in American claims against Mexico. The United States agreed to honor the property rights of current inhabitants of the ceded territories, though the process was unevenly applied, and most residents lost their land over time. The last U.S. forces evacuated Mexico in August 1848.

Firm presidential leadership, competent generalship, contributions by junior officers trained at West Point, and superior field artillery contributed to the American victory, as did Mexican disorganization and strategic errors. Scott's advance on Mexico City ranks as a brilliantly executed campaign: he did not lose a single man in his amphibious landing near Veracruz; he daringly cut his lines to the coast in order to consolidate his army; he conciliated the Mexican people by keeping his troops under tight discipline; and, finally, he conserved manpower by circumventing several Mexican strongpoints.

The support of the American people, however, may have been the most decisive factor in the U.S. victory. Some did oppose the war, including pacifists, New England abolitionists (who wrongly saw the war as a southern plot to extend slavery), and antiexpansionists in the Whig party such as Congressman Abraham Lincoln of Illinois. But prowar enthusiasm predominated, allowing the U.S. government to raise more than 75,000 volunteer troops. During the war, Congress authorized a substantial expansion of the regular army, but American success depended upon volunteers.

The U.S. war record, however, was by no means unblemished. Although only 1,721 American soldiers were killed in combat, nearly 11,000 died of disease. Over 8 percent of U.S. enlisted men deserted, a higher percentage than in any other American foreign conflict. President Polk, a partisan Democrat, allowed politics to influence his military appointments. The campaign was marred by disputes between army and navy officers, friction between volunteers and regulars, and confusion about volunteers' enlistment terms. Bitter infighting among U.S. officers over rank and postbattle reports led to courts‐martial and even the removal of Scott from command. U.S. troops, most notoriously Texas Rangers serving with Taylor, committed crimes against the property and persons of Mexican civilians. The war also aroused racist passions in the United States. Starting in the Summer of 1847, some U.S. expansionists began calling for the United States to take over all of Mexico, but Polk's administration settled for a considerably smaller conquest—in part because of a popular outcry against absorbing multitudes of mixed‐race Mexicans into the American body politic. Most importantly, the never‐passed Wilmot Proviso, introduced by Pennsylvania congressman David Wilmot in August 1846 as an amendment to an appropriations bill, helped set the stage for the Civil War. By proposing to prohibit slavery in any territory acquired from Mexico, the measure renewed debate about slavery expansion—the issue often viewed as the most important cause of the Civil War.
See also Antebellum Era; Antislavery; Civil War: Causes; Compromise of 1850; Democratic Party; Racism; Slavery: Development and Expansion of Slavery; Texas Republic and Annexation.

Bibliography

Otis A. Singletary , The Mexican War, 1960.
Frederick Merk , Manifest Destiny and Mission in American History, 1963.
K. Jack Bauer , The Mexican War, 1974.
Robert W. Johannsen , To the Halls of the Montezumas: The Mexican War in the American Imagination, 1985.
John S.D. Eisenhower , So Far from God: The War with Mexico 1846–1848, 1989.
James M. McCaffrey , Army of Manifest Destiny: The American Soldier in the Mexican War, 1846–1848, 1992.

Robert E. May