https://www.ancient.eu/Tenochtitlan/ - Ancient Encyclopedia entry that covers the city of Tenochtitlan, the capital of the Aztec Empire. The article explains why the city is significant and how big the city was at its peak.
https://www.youtube.com/watch?v=_-96fKZGQVs – Khan Academy video that gives an overview of the Aztec Empire. It contextualizes their placement in the timeline of world history and describes why they are unique.
https://www.youtube.com/watch?v=UO5ktwPXsyM –TED-Ed provides an in-depth overview of the Inca Empire, tapping into the expansion of the empire and its various leaders.