[Symmetry]

Basically malaria was unknown in the Americas before western explorers brought it over. From there it became very prevalent in some places such as the Amazon and essentially made mass agriculture impossible there. Then pretty much everyone starved. There were also things like smallpox that devastated people everywhere in the Americas but those were more a one time thing, people were able to rebuild after they passed.

[scrollaway]

Good video on that, which a lot of people might have seen but still worth linking:

https://www.youtube.com/watch?v=JEYh5WACqEk

[cubano]

Isn't a devastating, long-term drought a recent and popular theory as well, decimating many Central and South American tribes such as the Mayans and the Aztec?

[1]http://science.time.com/2012/11/09/mayans/

[duaneb]

I believe the drought predated contact by ~7-800 years. Definitely explains the decline of the Mayans, but not really relevant to discussing the effects of Columbian contact.

[big_youth]

The Aztec were destroyed by the spanish, particularly Hernán Cortés.