After Mexican soldiers clashed with U.S. troops in disputed territory along the Rio Grande River in 1846, President James Polk led America into the war he had avidly sought. His purpose: snatching California and the Southwest from Mexico so that America could realize its “Manifest Destiny.” American troops won every battle in northern Mexico, and then, after an amphibious landing at Vera Cruz, marched to Mexico City.

The peace treaty gave Polk everything that he wanted: more than 500,000 square miles of California and the New Mexico territory for a mere $15 million. But the two-year war cost $100 million, more than 12,000 American lives, and eventually, popular support. More than 50 future Civil War generals received their baptism by fire in Mexico, including Ulysses Grant, George McClellan, George Thomas, Robert E. Lee, James Longstreet, and Thomas “Stonewall” Jackson.”

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