The Mexican Cession of 1848 is a historical name in the United States for the region of the present day southwestern United States that Mexico ceded to the U.S. in 1848, excluding the areas east of the Rio Grande, which had been claimed by the Republic of Texas, though the Texas Annexation resolution two years earlier had not specified Texas's southern and western boundary.

The U.S. had taken actual control of the Mexican territories of Santa Fe de Nuevo México and Alta California in 1846 early in the Mexican-American War, and Mexico acknowledged the loss of Texas, New Mexico, and California in the Treaty of Guadalupe Hidalgo, which was signed on February 2, 1848, ratified by the U.S. Senate on March 10, 1848, and by the Mexican government on May 19, 1848.

Background

The cession of this territory from Mexico was a major goal of the war. California and New Mexico 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 United States troops invaded central Mexico and occupied the Mexican capital of Mexico City, but still no Mexican government was willing to ratify transfer of the northern territories to the U.S. It was uncertain whether any treaty could be reached. There was even an All of Mexico Movement proposing complete annexation of Mexico among Eastern Democrats, opposed by Southerners like John Calhoun who wanted additional territory for white Southerners and their black slaves but not the large population of central Mexico. Eventually Nicholas Trist negotiated the Treaty of Guadalupe Hidalgo ceding only California and New Mexico in early 1848 after President Polk had already attempted to recall him from Mexico as a failure. The U.S. Senate approved the treaty, rejecting amendments from Jefferson Davis to also annex most of northeastern Mexico and by Daniel Webster to not even take California and New Mexico.

The United States also paid $15,000,000 ($298,310,309 in 2005) for the land, and agreed to assume $3.25 million in debts to US citizens. The land ceded by Mexico is 14.9% of the total area of the current United States territory. 1.36 million km² (525000 square miles, or 55% of its pre-war territory) was lost by Mexico.

As of July 1, 2007, the states of California, Nevada, Utah, Arizona and New Mexico had a total population of 50,072,597 out of 305,986,357 nationwide, or 16.4% of the US population.

For the years between 1821, when Mexican independence was secured and the Texas Revolution in 1836, the Mexican Cession had formed approximately 42% of the country of Mexico; prior to that, it had been a part of the Spanish colony of New Spain for some three centuries. Beginning in the early seventeenth century, a chain of Spanish missions and settlements extended into the New Mexico region, mostly following the course of the Rio Grande from the El Paso area to Santa Fe.

Territory

The region includes all of the present-day states of California, Nevada, and Utah; as well as portions of:

• Arizona excluding the region later annexed in the Gadsden Purchase
• Colorado west of the boundary of the former Republic of Texas
• New Mexico west of the Rio Grande and excluding the Gadsden Purchase, and
• Wyoming west of the former Republic of Texas boundary and south of the 42nd parallel.

The treaty also specified the international border between Texas and Mexico as being at the Rio Grande (Río Bravo del Norte). Previously the portion of Texas between the Nueces River and the Rio Grande had remained disputed throughout the existence of the Republic of Texas. The United States had already claimed the area as part of the Texas Annexation in 1845. Mexico had recognized neither.

The portion of New Mexico east of the Rio Grande had been claimed by the Republic of Texas and is therefore usually shown as part of the Texas Annexation. In actuality New Mexico was never divided at the Rio Grande, was never controlled by the Republic of Texas, and was widely separated from Texas by the Comancheria which was not under either Anglo or Hispanic control. Stephen Kearny's U.S. Army of the West from Fort Leavenworth, Kansas took New Mexico without resistance in 1846 early in the Mexican-American War. It was quickly provided with its own territorial government and was never governed by the State of Texas.

Subsequent organization and the North-South conflict

Soon after the war started and long before negotiation of the new US-Mexico border, the question of slavery in the territories to be acquired polarized the Northern and Southern United States in the bitterest sectional conflict up to this time, which lasted for a deadlock of four years during which the Second Party System broke up, Mormon pioneers settled Utah, the California Gold Rush settled California, and New Mexico under a federal military government turned back Texas's attempt to assert control over territory Texas claimed as far west as the Rio Grande. Eventually the Compromise of 1850 preserved the Union, but only for another decade. Proposals included:

• The Wilmot Proviso,which was created by Senator David Wilmot, banning slavery in any new territory to be acquired from Mexico, not including Texas which had been annexed the previous year. Passed by the United States House of Representatives in August 1846 and February 1847 but not the Senate. Later an effort to attach the proviso to the Treaty of Guadalupe Hidalgo also failed.
• Failed amendments to the Wilmot Proviso by William W. Wick and then Stephen Douglas extending the Missouri Compromise line (36°30' parallel north) west to the Pacific, allowing slavery in most of present day New Mexico and Arizona, Las Vegas, Nevada, and Southern California, as well as any other territories that might be acquired from Mexico. The line was again proposed by the Nashville Convention of June 1850.
• Popular sovereignty, developed by Lewis Cass and Douglas as the eventual Democratic Party position, letting each territory decide whether to allow slavery.
• William L. Yancey's "Alabama Platform," endorsed by the Alabama and Georgia legislatures and by Democratic state conventions in Florida and Virginia, called for no restrictions on slavery in the territories either by the federal government or by territorial governments before statehood, opposition to any candidates supporting either the Wilmot Proviso or popular sovereignty, and federal legislation overruling Mexican anti-slavery laws.
• General Zachary Taylor, who became the Whig candidate in 1848 and then President from March 1849 to July 1850, proposed after becoming President that the entire area become two free states, called California and New Mexico but much larger than the eventual ones. None of the area would be left as an unorganized or organized territory, avoiding the question of slavery in the territories.
• The Mormons' proposal for a State of Deseret incorporating most of the area of the Mexican Cession but excluding the largest non-Mormon populations in Northern California and central New Mexico was considered unlikely to succeed in Congress, but nevertheless in 1849 President Taylor sent his agent John Wilson westward with a proposal to combine California and Deseret as a single state, decreasing the number of new free states and the erosion of Southern parity in the Senate.
• Senator Thomas Hart Benton in December 1849 or January 1850: Texas's western and northern boundaries would be the 102nd meridian west and 34th parallel north.
• Senator John Bell (with assent of Texas) in February 1850: New Mexico would get all Texas land north of the 34th parallel north (including today's Texas Panhandle), and the area to the south (including the southeastern part of today's New Mexico) would be divided at the Colorado River into two Southern states, balancing the admission of California and New Mexico as free states.
• First draft of the compromise of 1850: Texas's northwestern boundary would be a straight diagonal line from the Rio Grande 20 miles north of El Paso to the Red River at the 100th meridian west (the southwestern corner of today's Oklahoma).

• The Compromise of 1850, proposed by Henry Clay in January 1850, guided to passage by Douglas over Northern Whig and Southern Democrat opposition, and enacted September 1850, admitted California as a free state including Southern California and organized Utah Territory and New Mexico Territory with slavery to be decided by popular sovereignty. Texas dropped its claim to the disputed northwestern areas in return for debt relief, and the areas were divided between the two new territories and unorganized territory. El Paso where Texas had successfully established county government was left in Texas. No southern territory dominated by Southerners (like the later short-lived Confederate Territory of Arizona) was created. Also, the slave trade was abolished in Washington, DC (but not slavery itself), and the Fugitive Slave Act was strengthened.

References

1. Treaty of Guadalupe Hidalgo, Articles XII-XV
2. Table 1.1 Acquisition of the Public Domain 1781-1867
3. http://books.google.com/books?id=mNQ1AAAAIAAJ&pg=PA185&lpg=PA185&dq=34th+parallel+wilmot&source=web&ots=6E2_o5IEwy&sig=bQFK83qaH3FNzW71eSBq-GpwJ-c&hl=en&sa=X&oi=book_result&resnum=1&ct=result#PPA191,M1 Quarterly of the Texas State Historical Association, January 1904