The Mexican-American War

The Mexican-American War was a war between the Union and Mexico. The Union fought Mexico in hopes of the annexation of Texas and receiving New Mexico and California territories.

The war was provoked because of competing claims of Texas by Mexico and the United States. During the Texas Revolution, Texan rebels fought against Mexico to gain their independence. Texan rebel Lieutenant Colonel William Travis moved his troops into the Alamo, which was a mission and fort. Antonio Lopez de Santa Anna, the Mexican president, held a 12 day siege at the Alamo beginning from February 23 up to March 6, 1836. The siege ended when Mexican troops attacked the post. Six weeks later, Sam Houston, the rebels' commander in chief, and 900 men surprise attacked Mexican troops near the San Jacinto River. Santa Anna was captured and freed after he signed the Treaty of Velasco, which granted independence to Texas. However, after the Treaty of Velasco was signed, Mexico still refused to recognize Texas' independence. Although Northerners and Southerners disagreed on the annexation of Texas due to issues involving slavery, Texas was annexed by President James K. Polk on December 29, 1845.

The war began when Mexico became angered by John C. Fremont for leading an American military exploration party, which violated Mexican territorial rights. On April 24, 1846, Mexican troops crossed the Rio Grande and ended up killing 11 U.S. soldiers. Congress declared war against Mexico and Colonel Stephen Kearny was ordered to march his troops to Santa Fe, New Mexico. There, they met upper-class Mexicans who desired to join the Union, thus New Mexico became occupied by United States during the war. In June 1846, Fremont led a group of American settlers in seizing a town named Sonoma located in California. The rebels proclaimed the nation of the Bear Flag Republic. Colonel Kearny arrived and U.S. forces took control of California. The United States was able to take control of both New Mexico and California without even using much force.

The cause of the Mexican-American War was the idea of Manifest Destiny, which was the belief that the United States was predestined to expand to the Pacific Ocean and into Mexican and Native American territory. Many Americans believed that Manifest Destiny was necessary for the country's prosperity and growth. The only problem was that Mexico owned most of the territory to the west. Once Texas became annexed by the United States, the Mexican government became furious and a war between the two nations was bound to occur.

President James K. Polk's affairs with Mexico got worse after the annexation of Texas. Border disputes occurred between the United States and Mexico. The United States wanted a border that extended to the Rio Grande, while Mexico wanted the border of Texas to end at the Nueces River. In November 1845, John Slidell was ordered to go to Mexico City to negotiate with General Jose Herrera about purchasing California and New Mexico. When Slidell arrived though, General Jose Herrera refused to meet with him to negotiate. President Polk then ordered General Zachary Taylor to blockade the Rio Grande.

Although many Americans believed in Manifest Destiny, not many supported the idea of going to war with Mexico to expand the country. The Democrats supported Polk because it was a chance to expand slavery to the states that they would accumulate from the victory of the war. By expanding slavery to more states, the Democrats would then have more power than the Republicans in the government. The Republicans, on the other hand, did not want to go to war with Mexico due to the fact that the South would gain more political power. President Polk, who was a Democrat and a former slaveholder, saw expansion of the Union as a necessity. After John C. Fremont violated Mexican territorial rights, Mexico became angered because the United States repeatedly kept crossing over their borders without their permission. As a result, Mexico decided that it was time to go to war against the United States.