Which U.S. conflict was a direct result of the annexation of Texas?

The Mexican-American War was a direct result of the annexation of Texas because it heightened tensions between the United States and Mexico. After Texas gained independence from Mexico in 1836, it sought to join the United States. When Texas was officially annexed in 1845, Mexico viewed this act as an affront, considering Texas a rebellious province that had not been legitimately separated. The annexation rekindled disputes over the southern border of Texas, which went from the Nueces River to the Rio Grande. This territorial disagreement escalated into armed conflict when U.S. troops were sent to the disputed area, leading to the outbreak of war in 1846. The resulting conflict, known as the Mexican-American War, ultimately resulted in significant territorial gains for the United States and a formal recognition of Texas as a state.