Mexican-American War

(1846–1848)

   A war in which Mexico ceded the present-day area from Texas to California to the United States, establishing the boundary between the two nations at the Rio Grande River and extending the United States “from sea to shining sea.” Conflict over Texas and the American President James Polk’s expansionist politics precipitated hostilities on April 25, 1846. When both nations signed the Treaty of Guadalupe Hidalgo on February 2, 1848, the United States fulfilled its self-proclaimed Manifest Destiny to expand westward.

   Polk won the presidency on an expansionist platform in 1845, leading to the annexation of then independent Texas. As Texas became the 15th slave state, an infuriated Mexican government broke diplomatic relations with the United States; Mexico never recognized its former territory’s independence. In response, Polk incurred further ire by sending an envoy to Mexico City with an offer to settle Texas’s disputed lower boundary at the Rio Grande and purchase Mexico’s territories to the west. When the government refused to negotiate, Polk ordered General Zachary Taylor to advance his troops through the disputed area to the Rio Grande.

   Mexican cavalry, considering this an act of aggression, attacked an American patrol on April 25. Congress declared war on May 13, 1846. Polk argued that Mexico had shed “American blood on American soil.” Taylor proceeded to push southwest into Mexico along the Rio Grande to defeat troops at Palo Alto, Resaca de la Palma, and Monterrey and in February 1847, at Buena Vista against Mexican hero General Antonio Lopez de Santa Anna. A second force under General Stephen W. Kearney seized New Mexico and occupied California by January 1847. Finally, General Win-field Scott led an army from the coast to Mexico City, where he defeated Santa Anna in September 1847. Mexico ceded more than 500,000 square miles to the United States for $15 million and $3.25 million in American claims against the government. The United States became a continental power with vast natural resources and access to newly discovered gold in California.

   Territorial expansion had its costs. Approximately 13,000 Americans and 50,000 Mexicans died during the war, most from disease rather than bullets or bayonets. The conflict lasted much longer than expected, costing the United States close to $75 million. The war bitterly divided Americans along sectional lines; discredited many of the moderate voices who had previously held sway; contributed mightily to the breakdown of the two-party system; and helped bring about the American Civil War, which claimed in excess of 600,000 lives.

   FURTHER READING:

    Bergeron, Paul H. The Presidency of James K. Polk. Lawrence: University of Kansas Press, 1987;

    Pletcher, David M. The Diplomacy of Annexation: Texas, Oregon and the Mexican War. Columbia: University of Missouri Press, 1973;

    Weinberg, Albert I. Manifest Destiny: A Study of Nationalist Expansionism in American History. Baltimore: The Johns Hopkins University Press, 1935.

   JOHN FAITHFUL HAMER