1846–1848 United States–Mexico War

Mexico–American War was a conflict fought between the United States and México from 1846 to 1848, resulting in massive territorial losses for México. The war was directly linked to the United States’ expansionist ambition under the doctrine of “Manifest Destiny.”

After the Republic of Texas declared its independence in 1836, it was annexed by the United States in 1845, a move México labeled as an “act of aggression.” Disputes over the border further escalated: the United States recognized the Rio Grande as Texas’s southern boundary, while México upheld the Nueces River as the legitimate border. This contested territory, known as the “Nueces Strip,” became one of the immediate causes of the war.

Military Developments

President James K. Polk dispatched troops under the command of General Zachary Taylor to the border region. On April 24, 1846, Mexican cavalry attacked U.S. forces, prompting President Polk to declare it an act of aggression. On May 13, 1846, Congress formally declared war.

The U.S. war strategy unfolded in three phases:

1. Occupation of northern México and New Mexico,

2. Conquest of California,

3. Capture of Mexico City.

General Taylor achieved victories in battles such as Palo Alto, Resaca de la Palma, and Monterrey.

General Winfield Scott advanced toward Mexico City following the amphibious landing at Veracruz and captured the city in 1847.

In the California Theater, regions were brought under U.S. control with the contributions of General Kearny and John C. Fremont.

Treaty and Consequences

Treaty of Guadalupe Hidalgo (February 2, 1848)

Under this treaty, México ceded to the United States the territories of California, Arizona, New Mexico, Nevada, Utah, and part of Colorado and Wyoming (approximately 1.36 million km²).

México recognized the Rio Grande as the international boundary. The United States agreed to pay $15 million in compensation and assume México’s outstanding debts.

Gadsden Purchase (1854)

To resolve lingering border disputes after the war, México sold southern parts of New Mexico and sections of Arizona to the United States for $10 million.

Domestic and International Impacts

Effects on American Society

- The war drew criticism from anti-slavery factions in the United States. Politicians such as Abraham Lincoln questioned the legitimacy of the conflict.

- Ralph Waldo Emerson predicted that the United States would emerge from the war “poisoned”; this forecast was later interpreted as foreshadowing the Civil War that followed.

Effects on Mexican Society

- México lost approximately half of its territory.

- Political instability deepened.

- Santa Anna returned to power multiple times during the war but was again exiled due to his failed defenses.

Role of the Navy

The U.S. Navy blockaded key ports along the Gulf of México and the Pacific coast. The amphibious landing at Veracruz was the largest such operation in U.S. history up to that point and played a crucial role in enabling the success of ground forces.