The Mexican–American War, also known in the United States as the Mexican War, and in Mexico as the United States intervention in Mexico, was an invasion of Mexico by the United States Army from 1846 to 1848. It followed the 1845 American annexation of Texas, which Mexico still considered its territory because Mexico 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 Second Federal Republic of Mexico refers to the period of Mexican history involving a second attempt to establish a federal government in Mexico after the fall of the unitary Centralist Republic of Mexico in 1846 at the start of the Mexican-American War. It would last up until the Second French Intervention in Mexico led to the proclamation of the Second Mexican Empire in 1863.