The conflict ignited by the Westward Expansion in the United States was the Mexican-American War, which took place from 1846 to 1848. Fueled by the concept of Manifest Destiny, many Americans believed it was their divine right to expand across the continent. Tensions escalated over the annexation of Texas and border disputes, particularly when American troops were sent to disputed territories. The war concluded with the Treaty of Guadalupe Hidalgo, resulting in significant territorial gains for the U.S. This expansion, however, intensified sectional tensions regarding slavery, ultimately contributing to the outbreak of the Civil War.