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1844
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
1845
January 2-10 - Santa Anna attacks Puebla
January 14 - Santa Anna captured by government forces
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
April 5 - Mexican president Herrera sends Antonio López de Santa Anna into exile in Cuba
July - President James K. Polk orders General Zachary Taylor to march to Corpus Christi to defend Texas frontier, and dispatches a naval squadron to the Gulf of Mexico
July 4 - Texas convention votes in favor of annexation to the United States
November - U.S. minister John Slidell arrives in Mexico
December 14 - San Luís Potosí garrison calls for the overthrow of Herrera
December 30 - Government of José Joaquín Herrera collapses in Mexico City
1846
January 1 - The Yucatán declares its independence from Mexico and its neutrality in the war with the United States
January 4 - General Mariano Paredes takes the oath of office as president in Mexico City
January 13 - President Polk orders Zachary Taylor to march from Corpus Christi to the Rio Grande and orders a blockade of Vera Cruz
March - Taylor marches to Rio Grande; John Slidell leaves Mexico
March 18 - In Matamoros, Mexican General Francisco Mejia issues a proclamation threatening hostilities against U.S. troops
April - General Mariano Arista takes command of the Mexican Army of the North
April 25 - Thornton Affair - U.S. dragoons attacked by Mexican cavalry on east bank of Rio Grande
May 3-8 - Siege of Fort Brown
May 8 - Battle of Palo Alto; John Slidell meets with President Polk
May 9 - News arrives in Washington of the Thornton Affair
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
July 14 - U.S. forces occupy Camargo, Tamaulipas
July 28 - General Paredes deposed in Mexico City by Mariano Salas
July 30 - General Taylor issues orders for movement of troops from Fort Brown to Camargo
August - Pedro de Ampudia appointed commander of the Army of the North
August 16 - Santa Anna returns to Mexico from exile in Cuba
August 18 - U.S. forces under General Stephen W. Kearny occupy Santa Fe, New Mexico
August 19 - U.S. troops Camargo begins march to Monterrey, Nuevo Leon
September 21-24 - Battle of Monterrey
October 7 - Battle of Dominguez Rancho, Southern California
November 14 - U.S. Navy seizes Tampico
November 16 - U.S. forces occupy Saltillo; Battle of Natividad, Northern California
November 17 - Polk orders a seaborne invasion of Vera Cruz
December - Valentín Gómez Farías assumes the duties of acting president
December 6 - Battle of San Pasqual, California
December 25 - Battle of El Brazito, New Mexico
1847
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 11 - Acting President Valentín Goméz Farías issues edict confiscating church property
January 19 - Taos Revolt begins; U.S. territorial governor Charles Bent killed
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
March 9 - 10,000 U.S. troops land on beaches by Navy at Veracruz
March 21 - Polkos Revolt ends
March 22-27 - Siege and bombardment of Veracruz
March 29 - Mexican forces at Veracruz surrender
April 18 - Battle of Cerro Gordo; Battle of Tuxpan
May 15 - Scott occupies Puebla
May 20 - Santa Anna assumes the presidency
August 19 - Battle of Contreras (Padierna)
August 20 - Battle of Churubusco; San Patricio battalion captured
September 8 - Battle of Molino Del Rey
September 13 - Battle of Chapultepec
September 13-14 - Battle for Mexico City
September 14 - Siege of Puebla begins
September 15 - Santa Anna resigns as president of Mexico; U.S. forces under General Winfield Scott occupy Mexico City
October 9 - Battle of Huamantla
October 12 - Siege of Puebla ends
December 22 - Abraham Lincoln presents his "spot resolutions" in Congress, challenging Polks' reasons for declaring war against Mexico
1848
January 24 - Gold discovered at Sutter's Mill, northern California
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
June 3 - José Joaquín Herrera elected to two-year presidential term
July 4 - President Polk formally announces ratification of Treaty of Guadalupe Hidalgo
August 2 - Last U.S. troops leave Mexico
November - General Zachary Taylor elected 12th U.S. president