As predicted, this sparked condemnation from the Mexican government which had never recognized Texan independence. Both nations began preparing for war. Polk sent troops into the disputed border region between the Nueces River and the Rio Grande, began mobilizing the US Navy, and sent special envoy John Slidell to Ciudad Mexico. When Mexican journalists learned that Slidell was in fact attempting to negotiate the purchase of more Mexican territory, New Mexico and California, it inflamed nationalist sentiment and many citizens threatened to revolt against President José Joaquín Herrera. The negotiations went nowhere.
Polk’s cabinet was still divided on declaring war. Several secretaries were not willing to vote for war until attacked by Mexican forces. This occurred when General Zachary Taylor, who had crossed Mexico’s stated border, the Nueces, led his troops to the Rio Grande. Soon after refusing the Mexican commander’s order to withdraw, a skirmish broke out between troops. Taylor reported 16 casualties. Polk argued before Congress that Mexico had invaded US territory and “shed American blood on American soil.” Congress swiftly declared war on Mexico in 1846. The Mexican government was defiant, but still divided amongst itself. The army overthrew the current president and brought General Santa Anna back to power.
The war saw battles in California, New Mexico, and Texas, but the major offensive took place in Mexico’s heartland. US forces invaded and occupied Veracruz. Civilian deaths far outnumbered military casualties. US newspapers reported shocking abuses against civilians by American troops. General Winfield Scott fought several battles on the way to Ciudad Mexico, and eventually conquered its defenses. The occupation of the ancient city was not an easy task, as the citizenry continued its resistance through acts of sabotage and guerrilla warfare. Most US deaths were the result of disease rather than combat.
The Treaty of Guadalupe Hidalgo was signed on February 2, 1848. The United States purchased California, New Mexico, and Texas, half of Mexico’s territory, for 18.25 million dollars. The treaty obligated the US to protect the property of the Mexicans in their new possessions by giving them US citizenship or just compensation if they decided to leave the country. In reality, only the most elite Mexicans were able to retain their wealth, while the majority of the population suffered political, cultural, and often violent repression, including frequent lynchings.
Despite this brutal history, Mexican and indigenous communities resisted erasure and fought to retain their cultures and communities throughout the American Southwest.
Sources:
Treaty of Guadalupe Hidalgo (1848)- The National Archives (US)
The United States-Mexican War, 1846-1848- United States Foreign Policy History and Research Guide
Mexican War Timeline- National Parks Service
“Santa Anna, the Centralized State, and the War with the United States.” The Course of Mexican History. Susan M. Deeds, Michael C. Meyer, William L. Sherman. Oxford University Press. 11th ed. 2018.