April 25 - Thornton Affair. May 8 - Ballte of Palo Alto. Mexican forces crosses the Rio Grande at Palo Alto and a battle with the Americans ensues. May 9 - Battle of Resaca de la Palma. May - President Polk addresses Congress.
War is declared.
July 4 - Captain John C. Fremont proclaims the independence of California. 7 - Navy Commodore John D. Sloat takes Monterey, California. November 16 - Battle of Natividad. December 6 - Battle of San Pasqual. December 25 - Battle of El Brazito.