The document provides an overview of pre-Columbian civilizations in Mesoamerica and South America, including their size, ecosystems, diversity and development. It then focuses on the Aztecs and Incas, noting that both had advanced, orderly societies according to early Spanish accounts. For the Aztecs, it outlines their origin story, nature as a warring empire and hierarchical social structure. For the Incas, it summarizes their origin story of the Tahuantinsuyo empire, key rulers and the nature of their empire and cosmology.