quality:corruption
Mexican–American War

Mexico refused to recognize the independence of Texas in 1836, but the U.S. and European powers did so. Mexico threatened war if Texas joined the U.S., which it did in 1845. American negotiators were turned away by a Mexican government in turmoil. When the Mexican army killed 16 American soldiers in disputed territory war was at hand. Whigs such as Congressman Abraham Lincoln denounced the war, but it was quite popular outside New England.

The Mexican strategy was defensive; the American strategy was a three-pronged offensive, using large numbers of volunteer soldiers. Overland forces seized New Mexico with little resistance and headed to California, which quickly fell to the American land and naval forces. From the main American base at New Orleans, General Zachary Taylor led forces into northern Mexico, winning a series of battles that ensued. The U.S. Navy transported General Winfield Scott to Veracruz. He then marched his 12,000-man force west to Mexico City, winning the final battle at Chapultepec. Talk of acquiring all of Mexico fell away when the army discovered the Mexican political and cultural values were so alien to America's. As the Cincinnati Herald asked, what would the U.S. do with eight million Mexicans "with their idol worship, heathen superstition, and degraded mongrel races?"

The Treaty of Guadalupe Hidalgo of 1848 ceded the territories of California and New Mexico to the United States for $18.5 million (which included the assumption of claims against Mexico by settlers). The Gadsden Purchase in 1853 added southern Arizona, which was needed for a railroad route to California. In all Mexico ceded half a million square miles (1.3 million km) and included the states-to-be of California, Utah, Arizona, Nevada, New Mexico, and parts of Colorado and Wyoming, in addition to Texas. Managing the new territories and dealing with the slavery issue caused intense controversy, particularly over the Wilmot Proviso, which would have outlawed slavery in the new territories. Congress never passed it, but rather temporarily resolved the issue of slavery in the West with the Compromise of 1850. California entered the Union in 1850 as a free state; the other areas remained territories for many years.