TheMexican Cession (Spanish:Cesión mexicana) is the territory that Mexico ceded to the United States in theTreaty of Guadalupe Hidalgo in 1848 after theMexican–American War. It comprises the states ofCalifornia,Texas,New Mexico,Utah,Nevada, andArizona, and parts ofColorado,Oklahoma,Kansas, andWyoming in the present-dayWestern United States. Consisting of roughly 529,000 square miles (1,370,000 km2), not including Texas, the Mexican Cession was the third-largest acquisition of territory in U.S. history, surpassed only by the 827,000-square-mile (2,140,000 km2)Louisiana Purchase of 1803 and the later 586,000-square-mile (1,520,000 km2)Alaska Purchase from Russia in 1867.
Most of the ceded territory had not been claimed by theRepublic of Texas following its de facto independence in the1836 revolution. Texas had only claimed areas east of theRio Grande. Afterannexation into the U.S. and admission as a state in 1845, Texas's southern and western boundaries with the Mexican state ofSanta Fe de Nuevo México had not been defined by the U.S. Most of the ceded area was part of the Mexican province ofAlta California (Upper California) while the southeastern strip east of the Rio Grande had been part of the state of Santa Fe de Nuevo México. Mexico had controlled the ceded territories with considerable local autonomy. After theMexican War of Independence finished in 1821, the area had seen several revolts but the Mexican government sent few troops from central Mexico to suppress them. In 1846, U.S. PresidentJames K. Polk sent soldiers to occupy the disputed territory between theNueces River and the Rio Grande, starting the Mexican–American War. At the war's outbreak, the U.S. conducted a naval landing on Mexico's northeastern coast on theGulf of Mexico, and advanced into Nuevo México.
The northern boundary of the ceded territories was at the42nd parallel north of latitude which was originally decided by theAdams–Onís Treaty of 1821 signed by the United States and the Kingdom of Spain in 1821, and was further ratified by the successor independent state of Mexico in 1831 in theTreaty of Limits. The eastern boundary of the Mexican Cession was the former old Texas Republic claim of additional territory to the west. The southern boundary was set by the war-ending peaceTreaty of Guadalupe Hidalgo, which followed theGila River and the original Mexican boundaries between Alta California to the north, andBaja California and the Mexican state ofSonora to the south.
The question of whether future Western states formed out of these 1848 Mexican Cession lands would permit the institution of slavery was a major American political issue in the lead-up to theAmerican Civil War (1861–1865).
Alta California andSanta Fe de Nuevo México were captured soon after the start of the war and the last resistance there was subdued in January 1847, but Mexico would not accept the loss of territory. Therefore, during 1847, troops from the United States invaded central Mexico and occupied the Mexican capital ofMexico City, but still no Mexican government was willing to ratify the transfer of the northern territories to the U.S. It was uncertain whether any treaty could be reached. There was even anAll of Mexico Movement proposing complete annexation of Mexico among Eastern Democrats but opposed by Southerners likeJohn C. Calhoun who wanted the additional territory for their crops but not the large population of central Mexico.[citation needed]
EventuallyNicholas Trist forged theTreaty of Guadalupe Hidalgo, explicitly redefining the border between Mexico and the United States in early 1848 after President Polk had already attempted to recall him from Mexico as a failure. Although Mexico did not overtly cede any land under the treaty, the redefined border transferred Alta California and Santa Fe de Nuevo México to the control of the United States. Equally important, the new border also acknowledged Mexico's loss of Texas, both the core eastern portion and the western claims, neither of which had been formally recognized by Mexico until that time.[citation needed]
The U.S. Senate approved the treaty, rejecting amendments fromJefferson Davis to also annex most of northeastern Mexico and fromDaniel Webster to decline to take Alta California and Santa Fe de Nuevo México.[1] The United States paid $15 million ($482 million in 2016 dollars) for the damage caused by the war in Mexico's territory and agreed to assume $3.25 million in debts to U.S. citizens.[2]
The Mexican Cession as ordinarily understood (i.e. excluding lands claimed by Texas) amounted to 525,000 square miles (1,400,000 km2), or 14.9% of the total area of the current United States. If the disputed western Texas claims are also included, that amounts to a total of 750,000 square miles (1,900,000 km2). If all of Texas is included, since Mexico had not previously acknowledged the loss of any part of Texas, the total area ceded under this treaty comes to 915,000 square miles (2,400,000 km2).
Considering the seizures, including all of Texas, Mexico lost 55% of its pre-1836 territory in the Treaty of Guadalupe Hidalgo.[3] For only 15 years, from 1821 (whenMexican independence was secured) to the Texan Revolt in 1836, the Mexican Cession (excluding Texas) formed approximately 42% of the country of Mexico. Prior to that, it had been a part of the Spanish colony ofNew Spain for three centuries.
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Soon after the war started and long before negotiation of the newMexico–United States border, the question of slavery in the territories to be acquired polarized the Northern andSouthern United States in the bitterest sectional conflict up to this time, which lasted for a deadlock of four years, during which theSecond Party System broke up,Mormon pioneers settledUtah, theCalifornia Gold Rush settledCalifornia, and New Mexico-stationed federal troops turned back Texas's attempt to assert control over territory Texas claimed as far west as the Rio Grande. Eventually theCompromise of 1850 preserved the Union, but only for another decade. Proposals included:
It quickly became apparent that the Mexican Cession did not include a feasible route for atranscontinental railroad connecting to a southern port. The topography of the New Mexico Territory included mountains that naturally directed any railroad extending from the southern Pacific coast northward, to Kansas City, St. Louis, or Chicago. Southerners, anxious for the business such a railroad would bring (and hoping to establish a slave state beachhead on the Pacific coast),[5] agitated for the acquisition of railroad-friendly land at the expense of Mexico, thus bringing about theGadsden Purchase of 1853.
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