Signed in the Mexico City suburb of Guadalupe Hidalgo, the treaty ceded present-day California, Nevada, Utah, and parts of Arizona, New Mexico, Colorado, and Wyoming to the United States for $15 million. The transfer reshaped the map of North America, displacing tens of thousands of Mexican citizens and Indigenous peoples and setting the stage for later debates over slavery's expansion into the new territories.
Nicholas Trist, a State Department clerk whom President Polk had actually recalled in frustration, defied his own government's orders and stayed in Mexico to finish negotiating the treaty because he believed further delay would only worsen Mexico's position and inflame American appetite for even more land. His gamble paid off politically, if not personally — Polk was furious at his insubordination even while accepting the finished treaty.
Mexico lost roughly 55 percent of its pre-war territory, a staggering 525,000 square miles, in exchange for a payment that many Mexicans viewed as barely softening naked conquest. The treaty theoretically guaranteed property and civil rights to Mexican citizens who remained in the ceded lands, promises that were widely violated in the following decades as Anglo-American settlers pushed in.
The newly acquired territory reignited the volatile question of whether slavery would expand westward, a fight that would help pull the United States toward civil war within little more than a decade.