Treaty of Guadalupe Hidalgo Background:
With the Mexican-American War raging in early 1847, President James K. Polk was convinced by Secretary of State James Buchanan to dispatch a representative to Mexico to aid in bringing the conflict to an end. Selecting Chief Clerk of the State Department Nicholas Trist, Polk sent him south to join General Winfield Scott's army near Veracruz. Though Scott initially resented Trist's presence, the two men quickly reconciled and became close friends. As the war had been going favorably, Trist was instructed to negotiate for the acquisition of California and New Mexico to the 32nd Parallel as well as Baja California.
Trist Goes It Alone:
As Scott's army moved inland towards Mexico City, Trist's early efforts failed to secure an acceptable peace treaty. In August, Trist succeeded in negotiating a cease fire, but subsequent discussions were unproductive and the armistice expired on September 7. Convinced that progress could only be made if Mexico were a conquered enemy, he watched as Scott concluded a brilliant campaign with the capture of the Mexican capital. Forced to surrender following the fall of Mexico City, the Mexicans appointed Luis G. Cuevas, Bernardo Couto, and Miguel Atristain to meet with Trist to negotiate the peace treaty.
Unhappy with Trist's performance and inability to conclude the treaty earlier, Polk recalled him in October. In the six weeks it took for Polk's recall message to arrive, Trist learned of the appointment of the Mexican commissioners and opened talks. Believing that Polk did not understand the situation in Mexico, Trist ignored his recall and penned a sixty-five page letter to the president explaining his reasons for remaining. Pressing on with negotiations, Trist successfully concluded the Treaty of Guadalupe Hidalgo and it was signed February 2, 1848, in the Basilica of Guadalupe at Villa Hidalgo.
Terms of the Treaty:
Receiving the treaty from Trist, Polk was pleased with its terms and grudgingly passed it to the Senate for ratification. For his insubordination, Trist was terminated and his expenses in Mexico were not reimbursed. Trist did not receive restitution until 1871. The treaty called for Mexico to cede the land comprising the present-day states of California, Arizona, Nevada, Utah, and parts of New Mexico, Colorado, and Wyoming in exchange for a payment of $15 million. In addition, Mexico was to relinquish all claims to Texas and recognize the Rio Grande as the border.
Other articles of the treaty called for the protection of Mexican citizens' property and civil rights within the newly acquired territories, agreement on the part of the United States to pay American citizens debts owed to them by the Mexican government, and the compulsory arbitration of future disputes between the two nations. Those Mexican citizens living within the ceded lands were to become American citizens after one year. Arriving in the Senate, the treaty was heavily debated as some senators wished to take additional territory and others sought to insert the Wilmot Proviso to prevent the spread of slavery.
While the insertion of the Wilmot Proviso was defeated 38-15 along sectional lines, some modifications were made including a change to the citizenship transition. Mexican nationals in the ceded lands were to become American citizens at time judged by Congress rather than in one year. The altered treaty was ratified by the US Senate on March 10 and by the Mexican government on May 19. With the ratification of the treaty, American troops departed Mexico.
Besides ending the war, the treaty dramatically increased the size of the United States and effectively established the principle borders of the nation. Additional land would be acquired from Mexico in 1854 through the Gadsden Purchase which completed the states of Arizona and New Mexico. The acquisition of these western lands gave new fuel to the slavery debate as Southerners advocated for allowing the spread of the "peculiar institution" while those in the North wished to block its growth. As a result, the territory gained during the conflict helped contribute to the outbreak of the Civil War.