Introduction to Mexican War
Mexican War, 1846–48, a war between the United States and Mexico. As a result of its victory the United States gained an area of 529,017 square miles (1,370,148 km 2 ) from Mexico—the present states of California, Nevada, and Utah, and parts of Arizona, New Mexico, Colorado, and Wyoming. In addition, the United States gained permanent possession of more than 275,000 square miles (712,000 km 2 ) of disputed territory claimed by Texas after its independence. The acquisition of these vast lands by the United States intensified the debate between North and South concerning slavery in the territories and brought the nation closer to civil war.
Zachary Taylor, one of the heroes of the Mexican War, was elected President in 1848. Two other leading participants, Winfield Scott and John C. Frémont, later ran unsuccessfully for the Presidency. Franklin Pierce (President, 1853–57) and Jefferson Davis (Confederate President, 1861–65) advanced their political careers by Mexican War service. Many of the Civil War generals, including Robert E. Lee and U.S. Grant, took part in the war, gaining valuable military experience.
Background
The main underlying cause of the war was the annexation of Texas in 1845 by the United States. Texas had been a Mexican province, but rebelled in 1835. As a result of the Battle of San Jacinto (1836) Texas won its independence, though it was not recognized by Mexico. Soon afterward, Texas applied for admission to the United States. Mexico declared in 1843 that annexation would be equivalent to an act of war. After Congress passed a joint resolution for annexation, March 1, 1845, Mexico broke diplomatic relations. Texas was admitted on December 29, 1845.
The immediate cause of the war was a boundary dispute. Mexico claimed that the Nueces River was the southern boundary of Texas, while the United States had inherited Texas' claim of the Rio Grande as the border. President James Polk sent John Slidell as minister plenipotentiary to deal with the Mexican government, but it refused to receive him.
Thereupon Polk, on January 13, 1846, ordered Brigadier General Zachary Taylor to occupy the disputed territory. Taylor arrived there in March with nearly 4,000 men. A Mexican force faced him across the Rio Grande. On April 23, Mexican President Mariano Paredes declared a “defensive war,” and on April 25 Mexican troops crossed the river and attacked a cavalry patrol. Upon hearing the news, Congress voted to declare war. President Polk signed the war resolution on May 13, 1846.
The Fighting
The United States entered the war with an actual army strength of only 7,365 men. Congress authorized the President to increase the size of the regular army to 15,000 men and to raise 50,000 short-term volunteers. The volunteers signed mainly for periods of six months or one year. Mexico had a regular army of about 32,000, and a large federal territorial militia.
Taylor had already fought two battles before Congress declared war. On May 8, 1846, at Palo Alto, 2,300 United States troops defeated 6,000 attacking Mexicans. On May 9, at Resaca de la Palma, the Mexicans were again beaten, and fled across the Rio Grande.
Taylor crossed the Rio Grande on May 18. After receiving supplies and reinforcements, he arrived before Monterrey on September 17, with 6,000 men, to face 8,000 Mexicans. Fighting raged for days, and the city had to be taken street by street. Monterrey surrendered September 24, its defenders being granted an eight-week armistice while they withdrew to the south. President Polk was displeased and revoked the armistice.
In December, Brigadier General John E. Wool reinforced Taylor with about 2,000 men. He also received new men from training camps. In January, 1847, however 8,000 of Taylor's men were detached for Winfield Scott's central campaign. General Santa Anna (recently elected President of Mexico) learned of the weakening of Taylor's forces. Taylor's 4,800 men, encamped on the high ground of Buena Vista, near Saltillo, were attacked by 15,000 Mexicans. After two days of heavy fighting, February 22–23, the Mexicans were repulsed. They retreated, and fighting virtually ended in the north.
Soon after war began, a force under Brigadier General Stephen W. Kearny was ordered to take possession of New Mexico and California. Kearny occupied Santa Fe on August 18, 1846, established a provisional government, and continued west.
Meanwhile, Captain John C. Frémont, leading an expedition of frontiersmen and scouts, helped rebel settlers establish a “Republic of California.” In July and August, a United States naval squadron seized major California ports. Frémont cooperated with the squadron commander, Commodore Robert F. Stockton, in establishing a territorial government. Kearny arrived at San Diego in December, in time to help put down an uprising by Mexican settlers. Mexican authorities surrendered California on January 13, 1847.
In late 1846 Major General Winfield Scott, general in chief of the army, was given authority for an expedition against Mexico City. More than 10,000 troops came ashore without opposition near Veracruz on March 9, 1847. They were landed by a naval squadron that had been blockading Mexico's eastern coast. Veracruz surrendered on March 27.
The first real resistance occurred at Cerro Gordo, a narrow mountain pass, where Santa Anna had about 12,000 men. Scott turned the battle, April 17–18, into a rout by a flanking movement that enveloped the enemy. Thousands of prisoners and many weapons were taken. Scott paused at Puebla on May 15. His army had become depleted by illness and by the departure of thousands of volunteers whose terms of service had expired.
After building up his force again, Scott pushed forward in August, boldly cutting loose from his communications with Veracruz. Near Mexico City, his troops assaulted and captured fortified positions at Contreras and Churubusco, August 19–20. The fortifications of Molino del Rey were taken on September 8. Chapultepec, the main citadel, was stormed on September 13, and Mexico City was occupied the next day.
Peace Terms
Santa Anna resigned as president, and two months passed before a new Mexican government was organized. Nicholas Trist, chief clerk of the U.S. Department of State, signed a peace treaty at Guadalupe Hidalgo on February 2, 1848. Mexico recognized the Rio Grande as the southern boundary of Texas, and ceded its territory north of an irregular line extending from El Paso to the Pacific Ocean. The United States agreed to pay $15,000,000 for the territory ceded, and to assume up to $3,250,000 of claims previously made by United States citizens against Mexico.
Polk accepted the treaty and forwarded it to the Senate. The Senate ratified it on March 10 by a vote of 38 to 14. Opposition came from two groups—those who feared the extension of slavery to the territory acquired, and those who wanted to annex all of Mexico or a larger part of it. The Mexican Congress ratified the treaty on May 25. United States casualties in the Mexican War numbered 1,721 who were killed or died of wounds; 11,155 who died of disease; 361 dead from other causes; and 4,102 wounded. Mexican casualties were greater, but the number is not known.
