The Mexican Cession, a pivotal moment in North American history, refers to the vast territory relinquished by Mexico to the United States in 1848. This transfer of land was formalized through the Treaty of Guadalupe Hidalgo, which officially concluded the Mexican-American War (1846-1848). Signed on February 2, 1848, in Guadalupe Hidalgo, a city to the north of Mexico City, the treaty redrew the map of the continent, granting the U.S. over half of Mexico’s pre-war territory. This acquisition included present-day California, Nevada, Utah, New Mexico, most of Arizona and Colorado, and portions of Oklahoma, Kansas, and Wyoming. Furthermore, Mexico conceded all claims to Texas and acknowledged the Rio Grande as the definitive southern border with the United States.
The Treaty of Guadalupe Hidalgo: A Turning Point
The Treaty of Guadalupe Hidalgo emerged from the aftermath of Mexico’s military defeat and the capture of Mexico City by U.S. forces in September 1847. Facing overwhelming pressure, the Mexican government sought terms to end the conflict. Negotiations were spearheaded by Nicholas Trist, the chief clerk of the U.S. State Department, who accompanied General Winfield Scott as a diplomat and representative of President James K. Polk. Despite previous failed attempts to negotiate peace with Santa Anna, Trist and Scott recognized the necessity of dealing with Mexico as a defeated nation. Trist engaged in discussions with a specially appointed Mexican commission, composed of Don Bernardo Couto, Don Miguel Atristain, and Don Luis Gonzaga Cuevas, representing the then-collapsed Mexican government.
President Polk had initially intended for negotiations to occur in Washington D.C., recalling Trist with this expectation. However, communication delays meant Trist received news of the Mexican commission’s formation before Polk’s recall reached him. Believing that Washington was out of touch with the realities in Mexico, Trist made the momentous decision to proceed with peace negotiations, directly defying the president’s orders. In a letter to his wife dated December 4, 1847, Trist articulated his conviction, stating his awareness of the “dreadful consequences to our country which cannot fail to attend the loss of that chance,” and affirmed his “decision is altogether my own.”
Trist’s defiance, undertaken with full awareness of the potential career repercussions, underscores his commitment to his principles and his assessment of the critical opportunity for peace. His actions immediately made him a figure of controversy within the United States.
Terms of the Mexican Cession
Under the treaty terms negotiated by Trist, the Mexican Cession formally transferred Upper California and New Mexico to the United States. This vast area encompassed present-day Arizona and New Mexico, along with parts of Utah, Nevada, and Colorado, as detailed in Article V of the treaty. Furthermore, Mexico relinquished all claims to Texas and recognized the Rio Grande as the established southern boundary of the United States, also stipulated in Article V.
In exchange for this extensive land acquisition, the United States agreed to pay Mexico $15,000,000, characterized as “in consideration of the extension acquired by the boundaries of the United States,” as outlined in Article XII of the treaty. Additionally, the U.S. assumed responsibility for settling debts owed to American citizens by the Mexican government, as stated in Article XV.
Further provisions of the Treaty of Guadalupe Hidalgo addressed the protection of property and civil rights for Mexican nationals residing within the newly defined U.S. boundaries (Articles VIII and IX). The treaty also included a commitment from the United States to police its borders (Article XI) and mandated compulsory arbitration for future disputes between the two nations (Article XXI).
Ratification and Aftermath
Trist promptly dispatched a copy of the treaty to Washington, compelling President Polk to decide whether to reject the successful, albeit unauthorized, work of his subordinate. Polk ultimately chose to submit the treaty to the Senate. On March 10, 1848, the Senate reluctantly ratified the treaty by a vote of 34 to 14. However, during ratification, Article X, which guaranteed the protection of Mexican land grants, was removed. Following ratification, U.S. troops withdrew from the Mexican capital.
To implement the treaty’s boundary demarcation, Colonel Jon Weller and surveyor Andrew Grey were appointed by the U.S. government, and General Pedro Conde and Sr. Jose Illarregui by the Mexican government. Their task was to survey and establish the border. A subsequent agreement, the Gadsden Purchase of December 30, 1853, slightly adjusted the border, adding 47 boundary markers to the initial six. Many of these markers were rudimentary stone piles, while a few were more substantial with inscriptions.
Over time, the precise locations of these markers became disputed, with both countries alleging relocation or destruction. To resolve these issues, a convention in the 1880s led to a resurvey, confirming the need for clear boundary demarcation. This resulted in the establishment of the International Boundary Commission, tasked with relocating and remarking the boundary line. The U.S. commissioners even employed a survey photographer to document each monument erected or relocated by the U.S. section.
The Mexican Cession remains a significant event in the history of both the United States and Mexico. It dramatically expanded the territory of the U.S. and had lasting consequences for the cultural and political landscapes of both nations. The Treaty of Guadalupe Hidalgo and the Mexican Cession continue to be studied and debated, reflecting their enduring impact on the relationship between the United States and Mexico.
