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Clarifications: Each clarification provides an explanation of an indicator/objective to help teachers better understand the skills and/or concepts.

Standard 5.0 History

Topic C. Conflict between Ideas and Institutions

Indicator 2. Analyze the emerging foreign policy of the United States

Objective d. Explain causes and effects of the Mexican-American War


In its quest to achieve its “manifest destiny,” the United States long coveted the Mexican territories of California (for its Pacific ports and mineral deposits), New Mexico, and Texas (for its agricultural lands). President James Polk offered to purchase the territories from Mexico twice, but Mexico refused. Finally, in 1846, President Polk manipulated a border dispute to draw Mexico into outright war.

In 1845, the United States annexed Texas, which Mexico had never recognized as an independent country, and sent troops to take up positions along the Rio Grande. While the United States claimed the Rio Grande was the Texas-Mexico border, Mexico claimed the border lay farther north and that the Rio Grande was in Mexican territory. As President Polk had calculated, the stationing of troops along the Rio Grande provoked Mexico to attack and presented the United States with an opportunity to declare war as a defense against Mexican “aggression.”

After the United States drove Mexican forces from Texas, seized control of California and New Mexico, and captured Mexico City, the Mexican government surrendered in 1847. The Treaty of Guadalupe Hidalgo forced Mexico to give up half its territory to the United States, including Texas up to the Rio Grande, California, and New Mexico. In 1853, the United States paid Mexico $10 million for the remaining strip of land along the southern edge of Arizona and New Mexico in the Gadsden Purchase, bringing the United States to its present size.

In addition to increasing United States territory, the Mexican-American war also had other notable consequences. The addition of Texas fueled the already bitter debate over the extension of slavery. Also, the war served as the training ground for many of the Civil War’s most prominent generals.

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