Mexican-American War

The causes

In the 1830s, settlers from the United States moved in large numbers into Texas, then Mexican, and Texas declared its independence. Mexico refused to recognize it. Texas, now a republic, asked to join the United States, which annexed it in 1845. President James K. Polk also wanted California and New Mexico, and the disputed area between the Nueces and the Rio Grande became the scene of clashes in 1846.

Mexico became independent in 1821, but its government, often unstable, struggled to populate its northern provinces. It granted land to settlers from the United States, such as Stephen F. Austin, on condition that they converted to Catholicism. These settlers practised slavery despite the ban decreed in 1829, and Mexico tried to slow their arrival by banning American immigration in 1830. In 1836, after the Texan revolt, Santa Anna's defeat at San Jacinto forced him to recognise the independence of Texas, a treaty the Mexican Congress refused to ratify. In 1845, President Polk sent John Slidell to propose buying California and New Mexico, but Mexico City refused.

The course of the war

In May 1846, the American Congress declared war on Mexico. Operations took place on several fronts: General Zachary Taylor led the first campaigns in northern Mexico, while American forces occupied New Mexico and California, where American settlers rose up.

In 1847, General Winfield Scott landed near Veracruz, then advanced toward the capital, fighting battles against the armies of Antonio López de Santa Anna. In September 1847, American troops took Mexico City; during the fighting for Chapultepec Castle, young cadets, the Niños Héroes, fought and several of them died. The Treaty of Guadalupe Hidalgo, signed in 1848, ended the war: Mexico ceded California, New Mexico and other territories, recognized the Rio Grande as the border of Texas, and the United States paid 15 million dollars.

As early as June 1846, American settlers in California proclaimed a short-lived "Bear Flag Republic". In New Mexico, General Stephen W. Kearny occupied Santa Fe in August. In northern Mexico, General Zachary Taylor crossed the Rio Grande and took Monterrey in September 1846, after several days of urban fighting. The Texan volunteers, poorly disciplined, were often hard to command, and operations were scattered over fronts far from one another. This division reflected Polk's determination to occupy the northern provinces quickly, before any negotiation.

In February 1847, Taylor repelled at Buena Vista a Mexican army led by Santa Anna, whose attack failed. Meanwhile, Winfield Scott landed at Veracruz in March and besieged the city, which surrendered after three weeks of bombardment. He then marched inland and defeated Santa Anna at Cerro Gordo in April 1847, by going around a Mexican position reputed impregnable through the heights. This success opened the road to Mexico City, because the Mexican army lost much of its artillery and many prisoners.

The San Patricio Battalion, made up of American deserters, mostly Catholics of Irish origin, fought in the Mexican army. The Americans prevailed at Contreras and Churubusco, in August 1847, before entering Mexico City, where fighting took place street by street. During the occupation, American authorities had to deal with guerrilla warfare, and the civilian population suffered requisitions and reprisals. The capture of the capital, in September 1847, did not end the war: peace negotiations lasted several more months.

The consequences

Mexico lost nearly half of its territory, a wound that left a lasting mark on its national history. The United States gained a vast territory reaching the Pacific, and the discovery of gold in California, in 1848, later drew many migrants. The debate over extending slavery into the new territories divided the country and fed the tensions that would lead to the American Civil War.

Officers who distinguished themselves in this war, such as Ulysses S. Grant and Robert E. Lee, later commanded the Union and Confederate armies during the Civil War. Abraham Lincoln, then a member of Congress, criticised the origin of the conflict, and American historiography long presented the war as a patriotic success before historians began to examine it more critically. In Mexico, the defeat fostered a lasting nationalism, and the memory of the lost territories remains present in political debates. In 1853, the Gadsden Purchase completed the present border with a strip of land south of Arizona.

Timeline

1. 1845The United States annexes Texas
2. 1846The American Congress declares war on Mexico
3. 1847General Winfield Scott's troops take Mexico City
4. 1848Treaty of Guadalupe Hidalgo: Mexico cedes California and New Mexico

Key figures

• James K. Polk, American president during the war, advocate of westward expansion
• Zachary Taylor, American general, victor in northern Mexico
• Winfield Scott, American general who took Mexico City in 1847
• Antonio López de Santa Anna, president and commander of the Mexican armies, defeated several times