December 29, 1845 – Texas is annexed as a state.
January 1, 1846 – President Polk orders General Zachary Taylor to march to the Rio Grande River to protect Texas from any invasion by Mexican troops.
April 25-26, 1846 – Thornton Affair – Resulting in a Mexican victory, this battle occurred in the disputed borderlands of South Texas, instigating Congress to declare war on Mexico.
May 3-9, 1846 – Siege of Fort Texas – American forces withstand Mexican Army attacks.
May 8, 1846 – The Battle of Palo Alto occurred when the Mexican Army, under Mariano Arista in the disputed land between the Rio Grande and Nueces River, engaged an American army attempting to lift the aforementioned Siege of Fort Texas. Resulted in an American victory.
May 9, 1846 – In the Battle of Resaca de la Palma near Brownsville, Texas Mariano Arista is defeated by General Zachary Taylor.
May 13, 1846 – Congress declares war on Mexico.
May 18, 1846 – Occupation of Matamoros – U.S. troops occupy Matamoros, Tamaulipas, Mexico with no resistance. More than 300 sick and wounded Mexicans are captured in the hospitals.
July 4, 1846 – Captain John C. Fremont proclaims the independence of California.
July 7, 1846 – The Battle of Monterey, California results in a U.S. victory when Navy Commodore John D. Sloat occupies the city.
July 8, 1846 – Nava Commodore John D. Sloat seizes Yerba Buena (modern San Francisco.)
July 14, 1846 – The U.S. occupies Camargo, Tamaulipas, Mexico.
August 18, 1846 – Battle of Santa Fe – General Kearny occupies Santa Fe, New Mexico.
September 21-23, 1846 – In a second Battle of Monterey, California, General Zachary Taylor forces Pedro de Ampudia to surrender Monterrey.
September 22-30, 1846 – Siege of Los Angeles – Led by General José María Flores, Californios and Mexicans retake Los Angeles, California resulting in a Mexican victory.
September 26-27, 1846 – In the Battle of Chino, Californios defeat and capture 24 Americans, led by Benjamin D. Wilson, who were hiding in an adobe house in Rancho Santa Ana del Chino, near present-day Chino, California.
October 7, 1846 – In the Battle of Dominguez Rancho, California, Californios, led by José Antonio Carrillo, defeat 203 US Marines led by U.S. Navy Captain William Mervine.
October 24-26, 1846 – First Battle of Tabasco – Commodore Perry makes a demonstration against Tabasco, Mexico resulting in an inconclusive victory.
November 14, 1846 – Occupation of Tampico, Tamaulipas Mexico – Occupation is made by the U.S. Navy.
November 16, 1846 – Battle of Natividad – Taking place in the Salinas Valley in northern California, this skirmish resulted in an American victory. ALSO, The U.S. Army occupies Saltillo, Coahuila, Mexico.
December 6, 1846 – Battle of San Pasqual – Californeros and Presidial Lancers defeat General Kearny.
December 16, 1846 – The Mormon Battalion captures Tucson, Sonora and occupies her for a day or two.
December 25, 1846 – Battle of El Brazito – Also called the “Battle of Temascalitos” in Spanish, Mexican forces attack El Brazito, New Mexico, but the U.S. forces prevail under Colonel Alexander William Doniphan.
January 2, 1847 – The Battle of Santa Clara Fought in California, resulting in a U.S. victory.
January 8, 1847 – The Battle of Rio San Gabriel is fought as part of a series of battles for control of Los Angeles, California . The skirmish results in an American victory.
January 9, 1847 – Battle of La Mesa – The last conflict before U.S. forces enter Los Angeles, California results in a U.S. victory.
January 24, 1847 – In the Battle of Cañada, General Sterling Price defeats insurgents in New Mexico. ALSO, First Battle of Mora – A failed attack by American Forces on Mora, New Mexico is led by Israel Hendley.
January 29, 1847 – Battle of Embudo Pass – The last insurgent stand before the Siege of Pueblo de Taos in New Mexico results in an American victory.
February 1, 1847 – Second Battle of Mora – Another American expedition armed with howitzers succeeded in razing the village of Mora, New Mexico.
February 3-4, 1847 – Siege of Pueblo de Taos – Rancheros and Mexican Militia surrender to U.S. forces thus ending the Taos Revolt.
February 22-23, 1847 – Battle of Buena Vista – General Zachary Taylor fights Antonio López de Santa Anna south of Saltillo, Mexico in one of the largest battles of the war. Though heavily outnumbered, General Taylor’s 4,700 soldiers withstand the attack of Santa Anna’s 20,000 Mexicans.
February 28, 1847 – Battle of the Sacramento – Colonel Alexander Doniphan defeats a larger Mexican army before near the Sacramento River the capture of Chihuahua, Mexico.
March 9 – 29, 1847 – Siege of Veracruz – Beginning with Marine landings at Veracruz, Mexico, U.S. forces besiege and gradually encircle Mexican Marines and Coast Guard in the vicious twenty-day siege.
April 18, 1847 – The Battle of Cerro Gordo or Sierra Gordo took place near Xalapa, Veracruz, Mexico. General Winfield Scott’s U.S. troops flanked and drove Santa Anna’s larger Mexican army from a strong defensive position. ALSO, First Battle of Tuxpan – Commodore Matthew C. Perry seizes the port city of Tuxpan, Mexico on the Gulf coast.
April 22, 1847 – Capture of Perote – 54 Guns and mortars, and 500 muskets are captured at the Castle of Perote on the summit of the Eastern Cordilleras, 50 miles from Jalapa, Mexico. This was considered the strongest fortress in Mexico, except Veracruz.
May 26, 1847 – Battle of Red River Canyon – New Mexican insurgents fight a skirmish with United States troops which results in an American victory.
June 1847 – Second Battle of Tuxpan – Commodore Perry’s Mosquito Fleet engages Mexicans at Tuxpan for a second time resulting in a U.S. victory. Exact date unknown.
June 16, 1847 – Second Battle of Tabasco – Commodore Perry captures Villahermosa, the last port city on the Mexican Gulf Coast.
June 30, 1847 – Third Battle of Tuxpan – Perry’s Mosquito Fleet engages Mexicans for a third time, once again, resulting in an American victory.
July 6, 1847 – Battle of Las Vegas – New Mexican insurgents and United States soldiers fight at Las Vegas, New Mexico resulting in an American victory.
July 9, 1847 – Battle of Cienega Creek – New Mexicans and United States forces clash near Taos, New Mexico Resulting in a U.S. victory.
August 19, 1847 – Battle of Contreras – Also known as Battle of Padierna, Santa Anna failed to support the Mexican line at a critical moment resulting in a U.S. victory.
August 20, 1847 – Battle of Churubusco – Regular Mexican troops and Saint Patrick’s Battalion under Manuel Rincón hold a fortified monastery against General Winfield Scott. Just over half of the San Patricios are killed or captured, the rest retreat with the rest of the Mexican forces in the area.
September 8, 1847 – Battle of Molino del Rey – One of the bloodiest engagements of the Mexican-American War, the Americans lost nearly 800 men in an attempt to take a suspected cannon foundry. Still, the battle resulted in an American victory.
September 13, 1847 – Battle of Chapultepec – General Winfield Scott’s troops assault Chapultepec Castle west of Mexico City resulting in a U.S. victory.
September 13-14, 1847 – Battle for Mexico City – Fierce fighting takes place for Mexico City resulting in an American victory.
September 14, 1847 – Siege of Puebla – Mexican forces begin the siege of Puebla, Mexico, which will last for the next 28 days.
September 15, 1847 – Mexico City falls and U.S. forces occupy the city.
October 2, 1847 – Battle of Mulegé – Mexican forces led by Captain Manuel Pineda are defeated by a small detachment of American forces at Mulegé, Baja California Sur.
October 9, 1847 – Battle of Huamantla – U.S. relief column is able to reach Puebla, Mexico.
October 12, 1847 – The Siege of Puebla lifted by the relief force who were able to fight its way into the city.
October 19, 1847 – Skirmish at Atlixco – Also known as the “Atlixco Affair,” this skirmish results in an inconclusive victory.
October 31, 1847 – Bombardment of Punta Sombrero – The United States Navy schooner USS Libertad silences Mexican shore batteries in the Sea of Cortez.
November 16-17, 1847 – The Battle of La Paz, Mexico results in a Mexican defeat.
November 20-21, 1847 – Battle of San José del Cabo – Mexicans defeated by American forces at San Jose del Cabo, Mexico.
November 27 – December 8, 1847 – Siege of La Paz – A second Mexican attack on La Paz, Mexico ends in an American victory.
January 22 – February 14, 1848 – Siege of San José del Cabo – A failed Mexican siege of San Jose del Cabo.
January – August 1848 – Mexican partisans continued to resist the U.S. Army of Occupation. Formal fighting, however, had ceased by the end of January.
February 2, 1848 – The Treaty of Guadalupe-Hidalgo signed, officially ending the Mexican-American War. The treaty provided for the Mexican cession of 525,000 square miles to the United States in exchange for 15 million dollars.
March 9 – 16, 1848 – Battle of Santa Cruz de Rosales – General Sterling Price advances into Chihuahua after the Treaty of Guadalupe Hidalgo was already signed. On March 9, Price demanded the unconditional surrender of the town. When General Trias refused to comply, he laid siege and waited for the arrival of reinforcements. Little happened until March 16, when Price decided to carry the town by assault.