Did you know that San Diego wasn't ours until about 150 years ago? In fact, the entire southwestern area of the US, including California, Nevada, Utah, Arizona, and parts of New Mexico, Colorado, Wyoming, Texas, Oklahoma, and Kansas, once belonged to Mexico. All this land was achieved through the Mexican War, which led to the Mexican Cession; the Texas War for Independence, which led to the Texas Annexation; and the Gadsden Purchase. Of the mentioned, the Mexican War, fought between 1846 and 1848, was the most important, though all three played a part, in the fulfilling of Manifest Destiny. .
Manifest Destiny, or the "belief that the United States had the right and the duty to expand to the Pacific" (Davidson 774), was also the main cause for all three events. However, as with all wars, there were many different causes of the Mexican War. American settlers in Texas clashed with Mexican troops several times in rebellion to their laws, and this led to the Texas War for Independence. The Texas War for Independence lasted from 1835-1836. Although this war was won after the Battle of San Jacinto, Texas was not immediately annexed by the United States. The US feared that an annexation would lead to a war between Mexico and the US, and the North feared that Texas would become a slave state. However, after a decade of growth, "Congress passed a joint resolution admitting Texas to the Union [in 1845]" (Davidson 288). .
Following the annexation of Texas, the area between the Nueces River and the Rio Grande was claimed by both nations - America and Mexico. The Mexican War was a war for southwestern territory that the US was intent on possessing, either through money or through bloodshed. In January 1846, the Mexican ambush of an American scouting party in the disputed area forced President James K. Polk and Congress to choose the latter. Although people used Manifest Destiny as a justification for the Mexican War, there is no such thing as a justifiable war.
