5.3 - The Mexican-American War

The Mexican-American War (1846-1848) was an important event that stemmed largely from the U.S. annexation of Texas and the desire of the U.S. to expand westward to the Pacific Ocean.

Causes of the War:

• Annexation of Texas: The inclusion of Texas into the U.S. sparked immediate disputes over its border with Mexico, contributing directly to the onset of the war.

• Diplomatic Tensions: Following the U.S. annexation of Texas, disputes over the territory's southern border intensified, with Mexico claiming the Nueces River as the border and the U.S. claiming the Rio Grande.

• Polk’s Expansionism: President James K. Polk’s administration pushed for the acquisition of California and New Mexico, further straining relations with Mexico.

Immediate Triggers:

• Border Skirmishes: Hostilities began when a Mexican army unit attacked a U.S. patrol near the Rio Grande, killing 11 American soldiers, which President Polk used to justify a call for war.

Wilmot Proviso:

• Slavery Controversy: Introduced by David Wilmot in 1846, this legislative proposal aimed to prohibit slavery in any territory acquired from Mexico. It passed the House but was blocked in the Senate, showing the deep sectional divisions over slavery.

Consequences of the War:

• Treaty of Guadalupe Hidalgo (1848): Ended the war with Mexico ceding vast territories including California and New Mexico to the U.S. for $15 million and assumption of American claims against Mexico.

• Slavery Debate Intensifies: The acquisition of new territories reignited debates over slavery’s expansion, exemplified by the Wilmot Proviso, which sought to ban slavery in any new territories but failed in the Senate.

Link to Civil War:

• Sectional Tensions: The war exacerbated North-South tensions, with Northerners suspecting Southern motives in extending slavery, setting the stage for escalating conflicts that would eventually lead to the Civil War.