The Aztec moved to the Valley of Mexico in A.D. 1100. About 225 years later, Tenochtitlan, a swampy island in Lake Texcoco, became their capital and their population soon grew to 200,000. In 1430, the Aztec joined with nearby peoples to defeat the rulers of the Valley of Mexico, the Tepanec. But in the end, the Aztec battles created enemies who crushed their empire.

Like the Aztec, the Inca of southern Peru, created an empire by conquering their neighbors. In time, the Inca built 19,000 miles of roads as well as bridges linking mountain peaks. They devised canals to irrigate crops, which they grew on mountainside terraces. In 1532, civil war made it easy for the Spanish to defeat the Inca. By 1572, the empire fell.