The United States' war with Mexico was fought from 1846 to 1848; The expansion of America's "Manifest Destiny" was one of the main reasons for this conflict. The United States wanted the territory of Mexico, which included Arizona, California, Nevada, New Mexico, Utah, and parts of Colorado and Wyoming. There was still a dispute over Texas, which had been ceded by General Antonio Lopez de Santa Anna in exchange for his freedom after being captured during the Texas Revolution of 1836. The United States had offered to pardon Mexico for $3 million they owed American citizens for damages caused by the Mexican War of Independence and to pay another $25-30 million in exchange for Mexican territories in the United States. Mexico would refuse this agreement because it could not respect it. Its own government and political and public opinion agreed that selling its territories to the United States would stain the national honor. The origins of the Mexican-American War were the border conflicts between Texas and Mexico. Texas claimed land up to the Rio Grande as its border based on the Treaty of Velasco and Mexico refused to accept it by claiming the border as the Nueces River. U.S. President Polk ordered General Zachary Taylor and his forces south of the Rio Grande, while Mexico ordered the Americans to withdraw from their lands and return to the Nueces River. Taylor ignored the Mexicans' demands and built a fort on the banks of the Rio Grande, opposite the town of Matamoros, Tamaulipas. On April 25, 1846, an American patrol commanded by Captain Seth Thornton was attacked by a Mexican force of 2,000 men commanded by General Mariano Arista. The American patrol was defeated and this first engagement between the United States and Mexico was called the "Thornton Affair". This action gave ...... middle of paper ......n. The instability of the Mexican government and its inability to provide supplies, weapons, and ammunition to its army were part of the nation's defeat. The Mexican officer corps was the key player in the defeat due to its pursuit of personal glory, financial gain, and its negligent attitude toward its men. Although many in the U.S. government did not want to go to war, they fully supported their military and provided all the resources necessary to defeat Mexico. The leaders of the American forces had both senior and junior officers capable of leading without the intention of seeking glory or personal glory, but of setting an example for their men on the battlefield and in the camps. It was the stability of the American government and its willingness to fully support the war with good supplies and leadership that ultimately defeated its adversary in every phase of the war...