The most important war of all for Texas came in the early 19th century, and the common story heard in America is about rebellion against intolerance, oppression and Mexican cruelty. The Battle of the Alamo in particular, surrounded by legend and testimonies of heroism, is a textbook example of the fight for freedom, comparable to the Jewish defenders during the Roman siege at Masada. The words "martyrs" and "Mexican tyranny" are almost always present in the recounts, and “Remember the Alamo!” is both a slogan of self-glorification and martyrdom that remains one of the most famous phrases in America. Texas formally asked to be annexed by the United States in 1845. This annexation angered the Mexican government, which still considered Texas to be part of its territory. Mexico had previously warned that the annexation of Texas would cause Mexico to declare war on the United States.
When a Mexican patrol attacked American cavalry in the disputed area north of the Rio Grande, President Polk went to Congress for a declaration of war. The declaration passed on May 13, 1846. The war against Mexico was unpopular with the opposition Whig party, especially in the North. Opponents of the war denounced it as a war of aggression, and denied that there had been a valid reason for war. Small American military units were quickly able to occupy key points in California, including San Francisco and Los Angeles. Although California was sparsely populated, some Mexican inhabitants formed an effective resistance which was eventually put down in 1847 by American reinforcements. Subsequently, a larger American army was sent to invade central Mexico, and managed to capture the Mexican capital, Mexico City, on September 13, 1847. News of the capital falling caused it to retreat to try to retake the capital. After the defeat of the last Mexican army, major hostilities ended.
