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June 6 - U.S. Senate defeats treaty of annexation with Texas November - James K. Polk defeats Henry Clay to become eleventh president of the United States December 5-7 - Santa Anna deposed; José Joaquín Herrera elected as interim president of Mexico
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March 1 - U.S. President John Tyler signs the Brown Resolution, offering Texas terms of annexation March 4 - James Knox Polk is inaugurated as the eleventh president of the United States March 31 - In response to passage of the Brown Resolution, Mexico's minister to the U.S., Juan N. Almonte, requests his passports, breaking off diplomatic relations between the two countries
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May 3-8 - Siege of Fort Brown May 11 - President's war message read to Congress May 13 - United States declares war against Mexico May 18 - U.S. troops occupy Matamoros June 14 - Bear Flag revolt declared in California July 7 - U.S. naval forces occupy Monterey, California
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January 2 - Battle of Santa Clara, California January 8 - Battle of Rio San Gabriel (Los Angeles), California January 9 - Battle of La Mesa (Los Angeles), California January 24 - Battles of Cañada and Mora, New Mexico January 29 - Battle of Emudo Pass, New Mexico February 3-4 - Battle of Pueblo de Taos, New Mexico February 22-23 - Battle of Buena Vista (Angostura) February 26 - Polkos Revolt begins in Mexico City February 28 - Battle of the Sacramento, Northern Mexico
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February 2 - Treaty of Guadalupe Hidalgo signed February 4 - Last battle of the war fought at Santa Cruz de Rosales, New Mexico March - Santa Anna departs for exile in Jamaica March 10 - U.S. Senate ratifies Treaty of Guadalupe Hidalgo, with amendments May 25 - Mexican Congress ratifies Treaty of Guadalupe Hidalgo July 4 - President Polk formally announces ratification of Treaty of Guadalupe Hidalgo August 2 - Last U.S. troops leave Mexico