By the 1830s, the United States had begun the path toward its manifest destiny. However, to complete this vision of American expansion from the Atlantic to the Pacific, the nation had to acquire territory that was not yet in its possession. After numerous diplomatic offers presented to Mexico by President James Polk to acquire lands west of Texas, combined with a dispute over the geographic border between Texas and Mexico that ended with an ambush of American soldiers stationed at the Rio Grande, a war loomed between the United States and Mexico. When Texas was annexed into the United States in 1845, the U.S. government recognized the Rio Grande as the southern border of Texas. The Mexican government, however, recognized the Nueces River as the southern border of Texas, 150 miles to the north of the Rio Grande. When U.S. troops were mobilized into the Rio Grande Valley in 1846, the Mexican government saw it as an act of aggression and mobilized troops to the Rio Grande. An ensuing fight broke out, and the U.S. War with Mexico began in 1846. Lieutenant Ulysses S. Grant was stationed with the U.S. Army near Corpus Christi when orders were received by his commanding officer, Major General Zachary Taylor, to mobilize U.S. troops into Mexico along the Rio Grande after the outbreak of war. Lieutenant Grant fought in most major battles of the U.S.–Mexico War, and he received two promotions for gallantry, earning the rank of captain by the conclusion of the war.