I need help getting started on this extra credit essay on ancient economies.

The prompt is:

Research and describe the ancient Incan economy? How did they get so big? What did they produce? Did they have money? What kind of economic system did they have? How did they trade? What were their downfalls?

Please use in-text citations so that I can follow what info is coming from which sources. This way I can potentially use any quotes and sources in my essay.