There shall be firm and universal peace between the United States of America and the Mexican Republic, and between their respective Countries, territories, cities, towns and people, without exception of places or persons."

Following the American occupation of Mexico City on September 14, 1847, it was expected in the United States that a negotiated peace was not far behind. Mexico's government was in turmoil, with no one willing to immediately come forward and take responsibility for acceding to the American demands, which included not only the recognition of the right of Texas to annex itself to the United States, as well as fixing its boundary at the Rio Grande, but also the cession of New Mexico and both Upper and Lower California - nearly half the territory then claimed by Mexico.

 The person sent by the U.S. government to negotiate a treaty with Mexico was Nicholas Trist, a veteran diplomat who spoke Spanish, the result of an earlier foreign service post Trist held in Cuba. Upon arrival in Mexico in May 1847 Trist encountered two difficulties.

Later after the Battles of Contreras and Churubusco had been fought and won by the American army and Scott's troops were then only a few short miles from the gates of Mexico City, a truce was declared. For several days Trist met with Mexican commissioners. However, Mexicans rejected the proposed American terms and the truce broken. But the resulting takeover of Mexico City by Scott's army led to Santa Anna's  downfall.

  With Santa Anna out of the way, a new Mexican government was formed in November under the leadership of Manuel Peña y Peña. But, just as Trist was about to enter into serious negotiations, he received a dispatch recalling him to Washington. Obviously not understanding or appreciating the handicaps Trist had been forced to overcome first, President Polk had grown impatient with his envoy's lack of progress in the six months he'd been in Mexico. Then after a few minor arguments about the location of San Diego, the Treaty of Guadalupe Hidalgo was signed on February 2, 1848.