The Immediate Trigger
The Mexican-American War started after U.S. and Mexican troops clashed along the Rio Grande in April 1846. President James K. Polk cited the skirmish as an attack on American soldiers and asked Congress for a declaration of war.
Background and Border Dispute
The conflict grew from a disagreement over Texas’s southern border. After annexation, the U.S. claimed the Rio Grande as the limit, while Mexico insisted the border was the Nueces River. Tensions rose as troops moved into the contested zone.
Outcome and Significance
The war ended with the Treaty of Guadalupe Hidalgo in 1848. Mexico ceded a large portion of its northern territory, including present-day California and New Mexico, while the U.S. paid damages and assumed certain claims. The event reshaped North America’s map and deepened debates over slavery.
