Mexican American War

​During the 19^th century, U.S. Americans believed that they were chosen by God to expand west and eventually take over the entire North American continent. This belief was called Manifest Destiny. Manifest Destiny was a justification for the purchase of the Louisiana Territory and expansion into the Oregon Territory. When Texas became independent of Mexico in 1836, the U.S. saw this as an opportunity to expand its territory west again.

Many Texans agreed. Texas was populated with many migrants from the U.S. who saw becoming an official state as opportunity to grow its trading markets and receive protection from the U.S. Army. The issue of slavery, however, made things complicated. After the Missouri Compromise of 1820, any new state entered into the U.S. south of Missouri would be a state where slavery was legal (a slave state). Since Texas was a huge territory south of Missouri, many abolitionists opposed U.S. expansion into Texas because it would lead to the expansion of slavery. In the 1840s, the U.S. was led by a president greatly in favor of land expansion. In 1845, President Polk approved of a plan that would make Texas the 28th state of the union.

Polk and the United States were not yet done with goals of westward expansion. Texas and Mexico disagreed about their land borders. The U.S. used this disagreement as an opportunity. Polk sent representatives from the U.S. to buy the land in question from Mexico, but Mexico refused. Polk then sent the U.S. army to secure the land near the Rio Grande, which Mexico viewed as their own. Mexico fired on the U.S. troops, giving Polk a reason to officially declare war on Mexico in 1846.

The Mexican-American War ended two years later in 1846 as a massive military victory for the U.S. The war ended with the Treaty of Guadalupe Hildago in which the U.S. agreed to pay $15 million in exchange for land that would become the states of California, Nevada, New Mexico, Utah, most of Arizona, and parts of Colorado and Wyoming. The U.S. agreed to protect any Mexicans living in the territory by granting them citizenship.

​The Mexican-American war had many lasting effects. Gold would be discovered in California leading to the California Gold Rush, which quickened the development and population of the U.S. American west. It also brought the issue of slavery back into national discussion. Would slavery expand into the new territory gained from the war? The answer to this question would lead to attempts at compromise, bloodshed, and eventually the U.S. fighting a war with itself over the freedom of slaves.