The Treaty of Guadalupe Hidalgo officially ended the Mexican–American War (1846–1848). It was signed on the 2nd of February 1848 in the town of Guadalupe Hidalgo.
After the defeat of its army and the fall of the capital in September 1847, Mexico entered into peace negotiations with the U.S. envoy, Nicholas Trist. The resulting treaty required Mexico to cede 55 percent of its territory including the present-day states of California, Nevada, Utah, most of Arizona, and parts of New Mexico, Colorado, and Wyoming. Mexico also relinquished all claims for Texas and recognized the Rio Grande as the southern boundary of Texas.
In turn, the U.S. government paid Mexico $15 million "in consideration of the extension acquired by the boundaries of the United States" and agreed to pay debts owed to U.S. citizens by the Mexican government. Mexicans in areas annexed by the U.S. could relocate within Mexico's new boundaries or receive U.S. citizenship and full civil rights.
The United States ratified the treaty on 10 March and Mexico on 19 May. The ratifications were exchanged on 30 May, and the treaty was proclaimed on 4 July 1848.
The U.S. Senate ratified the treaty by a vote of 38–16. The opponents of this treaty were led by the Whigs, who had opposed the war and rejected manifest destiny in general, and rejected this expansion in particular. The amount of land gained by the United States from Mexico was further increased due to the Gadsden Purchase of 1853, which ceded parts of present-day southern Arizona and New Mexico to the United States.
Negotiators
Nicholas Trist negotiated the peace talks; Trist, the chief clerk of the U.S. State Department, accompanied General Winfield Scott as a diplomat and President James K. Polk's representative. After two previous unsuccessful attempts to negotiate a treaty with General José Joaquín de Herrera, Trist and General Scott determined that the only way to deal with Mexico was as a conquered enemy. Trist negotiated with a special commission representing the collapsed government led by José Bernardo Couto, Miguel de Atristain, and Luis Gonzaga Cuevas of Mexico.
Terms
Although Mexico ceded Alta California and Santa Fe de Nuevo México, the text of the treaty did not list territories to be ceded and avoided the disputed issues that were causes of war: the validity of the 1836 revolution that established the Republic of Texas, Texas's boundary claims as far as the Rio Grande, and the right of the Republic of Texas to arrange the 1845 annexation of Texas by the United States.
Instead, Article V of the treaty described the new U.S.–Mexico border. From east to west, the border consisted of the Rio Grande northwest from its mouth to the point where it strikes the southern boundary of New Mexico (roughly 32 degrees north), as shown in the Disturnell map, then due west from this point to the 110th meridian west, then north along the 110th meridian to the Gila River and down the river to its mouth. Unlike the New Mexico segment of the boundary, which depended partly on unknown geography, "to preclude all difficulty in tracing upon the ground the limit separating Upper from Lower California", a straight line was drawn from the mouth of the Gila to one marine league south of the southernmost point of the Port of San Diego, slightly north of the previous Mexican provincial boundary at Playas de Rosarito.
Comparing the boundary in the Adams–Onís Treaty to the Guadalupe Hidalgo boundary, Mexico conceded about 55% of its pre-war, pre-Texas territorial claims and now had an area of 1,972,550 km2 (761,610 sq mi).
In the United States, the 1.36 million km2 (530,000 sq mi) of area between the Adams-Onís and Guadalupe Hidalgo boundaries outside the 1,007,935 km2 (389,166 sq mi) claimed by the Republic of Texas is known as the Mexican Cession. That is to say, the Mexican Cession is construed not to include any territory east of the Rio Grande, while the territorial claims of the Republic of Texas included no territory west of the Rio Grande. The Mexican Cession included essentially the entirety of the former Mexican territory of Alta California, but only the western portion of Santa Fe de Nuevo Mexico, and includes all of present-day California, Nevada and Utah, most of Arizona, the western portions of New Mexico and Colorado, and the southwestern corner of Wyoming.
Articles VIII and IX ensured the safety of existing property rights of Mexican citizens living in the transferred territories. Despite assurances to the contrary, land grants by the Mexican government to its citizens were often not honored by the United States because of unilateral modifications to and interpretations of the Treaty and U.S. legal decisions. Land disputes between the descendants of Mexican land owners and Anglo Americans continued into the 21st century. The United States also agreed to assume $3.25 million (equivalent to $120.9 million today) in debts that Mexico owed to United States citizens.
The residents had one year to choose whether they wanted American or Mexican citizenship; over 90% chose American citizenship. The others moved to what remained of Mexico (where they received land) or, in some cases in New Mexico, were allowed to remain in place as Mexican citizens.
Article XII engaged the United States to pay, "In consideration of the extension acquired", 15 million dollars (equivalent to $560 million today), in annual installments of 3 million dollars.
Article XI of the treaty was important to Mexico. It provided that the United States would prevent and punish raids by Indians into Mexico, prohibited Americans from acquiring property, including livestock, taken by the Indians in those raids, and stated that the United States would return captives of the Indians to Mexico. Mexicans believed that the United States had encouraged and assisted the Comanche and Apache raids that had devastated northern Mexico in the years before the war. This article promised relief to them.
Article XI, however, proved unenforceable. Destructive Indian raids continued despite a heavy U.S. presence near the Mexican border. Mexico filed 366 claims with the U.S. government for damages done by Comanche and Apache raids between 1848 and 1853. In 1853, in the Treaty of Mesilla concluding the Gadsden Purchase, Article XI was annulled.
Results
The land that the Treaty of Guadalupe Hidalgo brought into the United States became, between 1850 and 1912, all or part of nine states: California (1850), Nevada (1864), Utah (1896), and Arizona (1912), as well as, depending upon interpretation, the entire state of Texas (1845), which then included part of Kansas (1861); Colorado (1876); Wyoming (1890); Oklahoma (1907); and New Mexico (1912). The area of domain acquired was given by the Federal Interagency Committee as 338,680,960 acres. The cost was $16,295,149 or approximately 5 cents an acre. The remainder (the southern parts) of New Mexico and Arizona were peacefully acquired under the Gadsden Purchase, which was carried out in 1853. In this transfer the United States paid an additional $10 million (equivalent to $300 million in 2025) for land intended to accommodate a transcontinental railroad. However, the American Civil War delayed the construction of such a route, and it was not until 1881 that the Southern Pacific Railroad finally was completed as a second transcontinental railroad, fulfilling the purpose of the acquisition.
Background to the war
Mexico had claimed the area in question since winning its independence from the Spanish Empire in 1821 following the Mexican War of Independence. The Spanish had conquered part of the area from the Indigenous peoples over the preceding three centuries. Still, powerful and independent Indigenous nations remained within that northern region of Mexico.
Most of that land was too dry and too mountainous to support a large population. About 80,000 Mexicans inhabited California, New Mexico, Arizona, and Texas during the period 1845 to 1850, with far fewer in Nevada, southern and western Colorado, and Utah. On 1 March 1845, U.S. president John Tyler signed legislation to authorize the United States to annex the Republic of Texas, effective on 29 December 1845. The Mexican government, which had never recognized the Republic of Texas as an independent country, had warned that annexation would be viewed as an act of war.
Both the United Kingdom and France recognized the Republic of Texas's independence and repeatedly tried to dissuade Mexico from declaring war against its northern neighbor. British efforts to mediate the quandary proved fruitless, in part because other political disputes (particularly the Oregon boundary dispute) arose between Great Britain (as the claimant of modern Canada) and the United States.
On 10 November 1845, before the outbreak of hostilities, President James K. Polk sent his envoy, John Slidell, to Mexico. Slidell had instructions to offer Mexico around $5 million for the territory of Nuevo México and up to $40 million for Alta California. The Mexican government dismissed Slidell, refusing to even meet with him. Earlier in that year, Mexico had broken off diplomatic relations with the United States, based partly on its interpretation of the Adams–Onís Treaty of 1819, under which newly independent Mexico claimed it had inherited rights. In that agreement, the United States had "renounced forever" all claims to Spanish territory.
Neither side took any further action to avoid a war. Meanwhile, Polk settled a major territorial dispute with Britain via the Oregon Treaty, which was signed on 15 June 1846. By avoiding any chance of conflict with Great Britain, the United States was given a free hand regarding Mexico. After the Thornton Affair of 25–26 April, when Mexican forces attacked an American unit in the disputed area, with the result that 11 Americans were killed, five wounded, and 49 captured, Congress passed a declaration of war, which Polk signed on 13 May 1846. The Mexican Congress, having already issued their own declaration of war on 23 April 1846.
Conduct of war
U.S. forces quickly moved beyond Texas to conquer Alta California and New Mexico. Fighting there ended on 13 January 1847 with the signing of the "Capitulation Agreement" at "Campo de Cahuenga" and the end of the Taos Revolt. By the middle of September 1847, U.S. forces had successfully invaded central Mexico and occupied Mexico City.
Peace negotiations
Some Eastern Democrats called for complete annexation of Mexico and recalled that a group of Mexico's leading citizens had invited General Winfield Scott to become dictator of Mexico after his capture of Mexico City (he declined). However, the movement did not draw widespread support. President Polk's State of the Union address in December 1847 upheld Mexican independence and argued at length that occupation and any further military operations in Mexico were aimed at securing a treaty ceding California and New Mexico up to approximately the 32nd parallel north and possibly Baja California and transit rights across the Isthmus of Tehuantepec.
Despite several military defeats, the Mexican government was reluctant to agree to the loss of California and New Mexico. Even with its capital under enemy occupation, the Mexican government was inclined to consider factors such as the unwillingness of the U.S. administration to annex Mexico outright and what appeared to be deep divisions in domestic U.S. opinion regarding the war and its aims, which caused it to imagine that it was actually in a far better negotiating position than the military situation might have suggested. A further consideration was the growing opposition to slavery that had caused Mexico to end formal slavery in 1829 and its awareness of the well-known and growing sectional divide in the U.S. over the issue of slavery. It, therefore, made sense for Mexico to negotiate to play Northern U.S. interests against Southern U.S. interests.
The Mexican negotiators also had intercepted a secret letter from Secretary of State Buchanan to Trist reiterating that annexing Baja California and acquiring American transit rights in the Isthmus of Tehuantepec were expendable American demands. With that knowledge, the Mexicans steadfastly refused to budge on either issue. (Chamberlin, Eugene [1963])
The Mexicans proposed peace terms that offered only the sale of Alta California north of the 37th parallel north — north of Santa Cruz, California, and Madera, California, and the southern boundaries of today's Utah and Colorado. Anglo-American settlers already dominated this territory, but perhaps more importantly from the Mexican point of view, it represented the bulk of pre-war Mexican territory north of the Missouri Compromise line of parallel 36°30′ north — lands that, if annexed by the United States, would have been presumed by Northerners to be forever free of slavery. The Mexicans also offered to recognize the freedom of Texas from Mexican rule and its right to join the Union but held to its demand of the Nueces River as a boundary.