The Mexican War of 1846-1848 was one of the most important wars in the history of the United States, but has since fallen into obscurity in the annals. It was the nation's first war fought on foreign soil—a war that supported the concept of “manifest destiny,” the United States' God-given right to claim territory for the establishment of a free democratic society (Stevenson 2009). Although many historians argue that the war was forced on Mexico by slaveholders greedy for new territory, President John Polk saw the war as an opportunity to defend the annexation of Texas, establish the Rio Grande as the border, and acquire the territories California Mexicans. and New Mexico (Stevenson 2009). The annexation of the newly formed republic of Texas sparked fierce debate on all sides. All the slave states wanted to bring Texas into the Union, but a number of free states opposed it because it would destroy the balance of power in Congress. Great Britain also denounced annexation because it wanted to stop American expansion (McGill 2009). The Mexican government, which continued to claim the disputed territory, repeatedly warned that if Texas became an American state, there would be war. Despite the political controversies and prospects of war, the annexation of Texas was important because Great Britain was negotiating an alliance with the Republic of Texas. This alliance would destroy the cotton trade in the South and halt American expansion (The Mexican War 2006). Newly elected President James Polk, a strong supporter of American expansion, sent John Slidell to Mexico to negotiate a settlement for the territories of New Mexico and California and to ask Mexico to recognize the Rio Grande River as the new Mexican-American border. It was important for the United States to establish its own border... middle of paper... imposed on Mexico by slave owners greedy for new territory, President John Polk saw the war as an opportunity to defend the annexation of The Texas, establish the Rio Grande as its border and acquire the Mexican territories of California and New Mexico. Opportunity to defend the annexation of Texas, establish the Rio Grande as the border, and acquire the Mexican territories of California and New Mexico. References McGill, S. (2009). The War for Texas Independence and the Annexation of Texas. War for Texas Independence and the Annexation of Texas, 1. Retrieved from EBSCOhost.Stevenson, K. (2009). The Mexican War. Mexican War, 1. Retrieved from EBSCOhost.The Mexican War. (2006). Current Events, 106(3), 2. Retrieved from EBSCOhost.Tindall, GB, & Shi, DE (2010). America, a narrative history (8th ed., Vol. 1). New York, NY: W. W. Norton & Company.