Amazon rainforest was transformed over 2,000 years ago by mysterious earthworks

As per population crashing, his general thesis were:

- Disease spreads faster than explorers (people who would create records)

- For many reasons, European diseases were more deadly to Americans than American diseases were to Europeans.

- It's a lot easier to conquer a people if they are in the midst of an epidemic. Imagine an immune army invading Europe in the midst of the Bubonic Plague.

- In South America, severe climate events triggered massive wars that destroyed agriculture, leading to population collapse.

As per the tech, I would argue it did spread. Remember corn, potatoes, peppers, tomatoes, avocados, peanuts, sunflowers, and beans all came from Indians. As did the idea of a free people — the basis for America itself! We just don't tend to associate these ideas with "technology" as much as we do wheels and hammers. Much of the Eurasian technology we celebrate today was impractical and unnecessary in the Americas (What good is a wheel if you're climbing the stairs to Machu Picchu? What good is a horse if its hooves rot in the jungle?).

All that being said, I would recommend the book even though I have extremely mixed feelings about it. It was one of the most frustrating books I've read in recent memory, but at the same time, the material is extremely fascinating to me. I definitely came away realizing how ridiculous the history of Americas I learned in school was, but I can't say I came away with a better view of what the Americas looked like either. I'm really hoping for more research and writing on this subject — I think we have a lot to learn from the Old Americas, especially wrt to agriculture, agroforestry, and managing wildlands.

Year X: European explorer #1 sails up a river/crosses mountains/etc and discovers a vast empire, huge cities, and marvelous civilizations that his European nation might trade with. He brings pigs with him and trades them to the natives for their cool stuff.

Year X+20: European explorer #2 follows the path of explorer #1. Then he's all "WTF, there's nobody here." But explorer #2 does discover, e.g., the giant earthworks that explorer #1 said were there - it's just the city on top of the earthworks doesn't exist.

He postulates that in years X+1 to X+19, the smallpoxalypse occurred and civilization collapsed. The remaining survivors are just roving tribal bands trying to survive in the remains of their old civilization.

(To make a fictional analogy, consider the current civilization in Georgia and then consider the civilization depicted on the Walking Dead. Mann's hypothesis is that most of what we know about American Indians consists of observing the Walking Dead and then drawing conclusions about their pre-apocalyptic civilization.)