Mexican–American War: American and Mexican forces clashed at the Battle of San Pasqual, a series of skirmishes near San Diego, California.

The Mexican–American War, also known in the United States as the Mexican War, was an invasion of Mexico by the United States Army. It followed the 1845 American annexation of Texas, which Mexico still considered its territory because it refused to recognize the Treaties of Velasco, signed by President Antonio López de Santa Anna after he was captured by the Texian Army during the 1836 Texas Revolution. The Republic of Texas was de facto an independent country, but most of its Anglo-American citizens who had moved from the United States to Texas after 1822 wanted to be annexed by the United States.

The Battle of San Pasqual, also spelled San Pascual, was a military encounter that occurred during the Mexican–American War in what is now the San Pasqual Valley community in the county of San Diego, California. The series of military skirmishes ended with both sides claiming victory, and the victor of the battle is still debated. On December 6 and 7, 1846, General Stephen W. Kearny's US Army of the West, along with a small detachment of the California Battalion led by Archibald H. Gillespie, engaged a small contingent of Californios and their Presidial Lancers Los Galgos, led by Major Andrés Pico. After U.S. reinforcements arrived, Kearny's troops were able to reach San Diego.

San Diego is a city on the Pacific coast of Southern California, adjacent to the Mexico–United States border. It is the eighth-most populous city in the U.S. and second-most populous city in California with a population of over 1.4 million, while the San Diego metropolitan area with over 3.3 million residents is the 18th-largest metropolitan area in the nation. San Diego is the county seat of San Diego County. It is known for its mild Mediterranean climate, extensive beaches and parks, long association with the United States Navy, and recent emergence as a wireless, electronics, healthcare, and biotechnology development center.