What did the agriculturally based southern economy lack

The Buffalo was the main source of food for Indian tribes for a long period of time. Their meat was the main ingredient on the "table" of every Indian. Without buffalo it was impossible to imagine a life of a member of some Indian tribe.

Explanation:

Francis Parkman, who is probably the most famous historian that wrote about Native Americans wrote this because he knew how important the buffalo meat was for them. Unfortunately, when the "white man" came, he killed practically all the buffalo in need for their fur, which was pretty expensive back then.