This document provides an overview of the two major civilizations in the Americas in 1491: the Incas and the Mexica (Aztecs). It notes that these empires had risen to power in the century before Columbus' arrival, and were the latest in a long line of cultures in Mesoamerica and the Andes dating back 4000 years. The document outlines some of the major pre-Columbian civilizations like the Olmecs, Zapotecs, and Teotihuacan, noting their advances in agriculture, architecture, and communications, as well as their development of writing systems independent of other world civilizations.