What was one of the causes of the Mexican-American War?

The annexation of Texas was a significant cause of the Mexican-American War due to a combination of political, economic, and territorial disputes. After declaring independence from Mexico in 1836, Texas sought to join the United States, which created tension between the U.S. and Mexico. The desire to expand westward, known as Manifest Destiny, was driving American sentiment toward acquiring Texas.

When Texas was officially annexed by the United States in 1845, Mexico viewed this as an act of aggression and a violation of its sovereignty. The movement of American settlers into Texas and subsequent annexation heightened tensions between the two nations, ultimately leading to conflicts over disputed territories. This culminated in military confrontations that spurred the declaration of war in 1846. Thus, the annexation of Texas directly contributed to the outbreak of the Mexican-American War by intensifying existing hostilities and territorial disputes between the U.S. and Mexico.