Mexican–American War: Six teenage military cadets known as Niños Héroes die defending Chapultepec Castle in the Battle of Chapultepec. American troops under General Winfield Scott capture Mexico City in the Mexican–American War.

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.

A cadet is a student or trainee within various organisations, primarily in military contexts where individuals undergo training to become commissioned officers. However, several civilian organisations, including civil aviation groups, maritime organisations, and police services, also designate their trainees as cadets.

The Niños Héroes were six Mexican military cadets who were killed in the defence of Mexico City during the Battle of Chapultepec, one of the last major battles of the Mexican–American War, on 13 September 1847. The date of the battle is now celebrated in Mexico as a civic holiday to honor the cadets' sacrifice.

Chapultepec Castle is located on top of Chapultepec Hill in Mexico City's Chapultepec park. The name Chapultepec is the Nahuatl word chapoltepēc which means "on the hill of the grasshopper". It is located at the entrance to Chapultepec park, at a height of 2,325 metres (7,628 ft) above sea level. The site of the hill was a sacred place for Aztecs, and the buildings atop it have served several purposes during its history, including serving as a military academy, imperial residence, presidential residence, observatory, and since February 1939, the National Museum of History. Chapultepec Castle, along with Iturbide Palace, also in Mexico City, are the only royal palaces in North America which were inhabited by monarchs.