As Americans waited impatiently for a final peace settlement, they grew increasingly divided over their war aims. Ultra-expansionists, who drew support from northeastern cities as well as from the West, wanted the United States to annex all of Mexico. Many Southerners, led by John C. Calhoun, called for a unilateral withdrawal to the Rio Grande. They opposed annexation of any of Mexico below the Rio Grande because they did not want to extend American citizenship to Mexicans. Most Democratic Party leaders, however, wanted to annex at least the one-third of Mexico south and west of the Rio Grande.
Then suddenly on February 22, 1848, word reached Washington that a peace treaty had been signed. Earlier in February, Nicholas Trist, a Spanish-speaking State Department official, signed the Treaty of Guadalupe Hidalgo, ending the Mexican War. Trist had actually been ordered home two months earlier by Polk, but he had continued negotiating anyway, fearing that his recall would be "deadly to the cause of peace."
According to the treaty, Mexico ceded to the United States only those areas that Polk had originally sought to purchase. Mexico ceded California, Nevada, Utah, New Mexico, and parts of Arizona, Colorado, Kansas, and Wyoming to the United States for $15 million and the assumption of $3.25 million in debts owed to Americans by Mexico. The treaty also settled the Texas border dispute in favor of the United States, placing the Texas-Mexico boundary at the Rio Grande River.
Ultra-expansionists called on Polk to reject the treaty. William Tecumseh Sherman called the treaty "just such a one as Mexico might have imposed on us had she been the conqueror." But a war-weary public wanted peace. Polk quickly submitted the treaty to the Senate, which ratified it overwhelmingly. The war was over.
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