A country of south-central North America. Southern Mexico was the site of various advanced civilizations beginning with the Olmec and including the Maya, Zapotec, Toltec, Mixtec, and Aztec cultures. Mexico was conquered by Cortés in 1521 and held by the Spanish until 1821. The Treaty of Guadalupe Hidalgo that ended the Mexican War (1846-1848) awarded all lands north of the Rio Grande to the United States. Mexico City is the capital and the largest city.