armed conflict fought on foreign soil. Polk believed the United States had a "manifest destiny" to spread across the continent from East Coast to West Coast. In 1846 until 1848 it had lost its roots in the annexation of Texas and the westward thrust of American settlers. President Polk wanted to secure the boundary dispute over the setting boundary at the Rio Grande and to the sale of northern California. He failed to realize Mexican politicians would not agree to the alienation of any territory, especially Texas. In December of 1845, the United States had annexed Texas, which had been part of Mexico prior to becoming independent. "In 1845 Congress admitted Texas to the Union as a slave state, but Mexico had never formally recognized Texas's independence" (1, 272). This annexation outraged Mexico because they still claimed it as their own. For this reason, Mexico broke off diplomatic relations with the United States as soon as Texas had entered the Union (1, 272). .
As a result of this, both Mexico and the United States had interpreted different facts over the location of the Texas boundary. According to Mexico, "Texas's southern boundary was the Nueces River, not the Rio Grandes claimed by Texas" (1, 272), "the Nueces River had always been Texas's boundary when it was a Mexican providence" (1, 272). Another cause of the Mexican War was the U.S.'s openly declared ambition to acquire California and New Mexico. The U.S. had offered to buy these territories from Mexico, and to pay compensation to U.S. citizens with unsettled claims against Mexico for property damages (1, 272). "Polk dispatched an emissary to Mexico offering to purchase the region, but the Mexican government refused to negotiate" (2, 473). Since they refused to negotiate, Polk decided to provoke them into starting war. "Polk hoped that, since he could not buy the territory he wanted, that at least Taylor's position on the Rio Grande would provoke the Mexican army into starting a war" (1, 272).