Treaty Signed: U.S. Gains California and Beyond

Mexico lost half its national territory in a single document. The Treaty of Guadalupe Hidalgo, signed on February 2, 1848, ended the Mexican-American War and transferred roughly 525,000 square miles to the United States, including present-day California, Nevada, Utah, and most of Arizona, New Mexico, Colorado, and Wyoming. The price was $15 million, about the cost of building a few warships. The war had begun in April 1846 after a border dispute along the Rio Grande, which the U.S. claimed as the boundary of the newly annexed Texas while Mexico insisted the border lay at the Nueces River, 150 miles to the north. President James K. Polk, who had campaigned on territorial expansion, sent troops into the disputed zone. When Mexican forces attacked an American patrol, Polk told Congress that Mexico had "shed American blood on American soil" and demanded a declaration of war. Congressman Abraham Lincoln challenged this claim, demanding to know the exact "spot" where blood had been shed. American forces under Generals Zachary Taylor and Winfield Scott won a series of decisive battles, culminating in the capture of Mexico City in September 1847. Mexican negotiator Nicholas Trist, whom Polk had actually recalled to Washington in frustration, ignored his recall orders and negotiated the treaty anyway, reasoning that further delay would only worsen Mexico’s terms. The treaty guaranteed the roughly 80,000 Mexicans living in the ceded territory full U.S. citizenship and property rights, promises that were widely violated in practice. The massive land acquisition reignited the slavery debate that would consume American politics for the next thirteen years, as each new territory forced the question: slave state or free? The Compromise of 1850, Bleeding Kansas, and ultimately the Civil War all grew from the soil Mexico had been forced to surrender.