Centralist Republic of Mexico
American territorial expansion to the Pacific coast was a major goal of U.S. President James K. Polk. In 1845, the United States of America annexed Texas, which had won independence from Centralist Republic of Mexico in the Texas Revolution of 1836. Mexico did not accept the annexation, while also continuing to claim the Nueces River as its border with Texas, and also still considering Texas to be a province of Mexico. In 1845, newly elected U.S. President James K. Polk sent troops to the disputed area, and a diplomatic mission to Mexico. After Mexican forces attacked American forces, the U.S. declared the Mexican–American War (1846–1848).