And the point of the book is that Balkanized geography makes countries more likely to want to adopt free markets whereas big continents will be more likely to adopt authoritarian state control.

Sounds like nonsense - the US straddles an entire continent. At the opposite geographical extreme we have Taiwan and Japan, both highly successful free markets.

The US was colonized, it didn't spring forth from pre-history this way. Diamond's theory is about the foundations of civilization and how they led to the broad strokes of history, not about modern events.

South America was colonized at the same time, but they didn't recognize rights and never amounted to much economically.

South America was pretty much entirely a jungle-covered mineral colony. Resource curse theory applies.

I'm not buying those excuses. SA failed to prosper because they had unfree economies. Chile has prospered when it went more free market, and regressed when it turned away from them.