Unfortunately, mixed in with all these wonderful new facts were occasional references to stuff I already knew. Lots of those references were wrong.
When describing the Spanish conquest of the Incas Mann mentioned that conquistador cavalry could have been beaten by Inca spearmen. Totally true. I've got enough books describing how pre-gunpowder infantry can defeat cavalry to fill a shelf of their own. But Mann's example to prove this is the Battle of Marathon. No way. Not only was the Persian army only 2-5% cavalry but it was the absence of the cavalry that triggered the Athenian attack.
Mann also talked up the fiber technology of the Incas by pointing out that some conquistadors laid aside their steel breastplates for native cloth armor. He implies the cloth would protect better against enemy attacks. Hardly. After winning against a force dozens of times their size without losing a single man the Spaniards likely thought the Incan chipped-stone weapons were less of a danger than heatstroke, or at least a mild enough danger to let comfort overrule security.
Another error was the description of carbon-14 dating. That was very odd considering the previous paragraph described it correctly. A typo? Or cutting and pasting an explanation without understanding it? At the very least it's evidence of carelessness.
Then there was the discussion of the Norte Chico civilization. Mann presented it as a rival of Sumer, making the Andes a co-equal cradle of civilization with Mesopotamia. But in 3000 BC Sumer had cities up to 24,000 people in size, while Caral had only 3000. It's not a counterpart of Sumer but of Catal Huyuk, which had 5-10,000 people in 7500 BC.
Mann also claimed the Norte Chico cities were unfortified. Let's look at one of their structures:
If you're leading a band of spearmen on a raid on there, which option would you pick?
1. Lead them 2 by 2 up the ramp while the defenders line the edge to shoot at you.
2. Climb up the side while the defenders drop rocks on you.
3. Say "heck with it" and go raid a little peasant village.
In fairness to Mann, "unfortified" could be the mistaken assessment of the archaeologists rather than the author. I've seen the same description of Catal Huyuk, which would be murder on a storming party.
What makes the errors bother me even more is the author's statement in the afterword about fixing errors from the first edition. If this stuff got through how bad was it before? It's normal for an author to inflate the importance of his topic but inflating the facts is bad. I don't mind Mann being a booster, and this book fills a major gap. The question is whether he goes too far for his facts to be trusted.
He certainly goes pretty far in his opinions. When discussing Aztec human sacrifice he equates it to the executions of criminals in Europe. Personally I find a huge moral difference between harshly punishing convicted criminals and hunting down innocents for the sole purpose of killing them horribly. Mann mourns the loss of the Aztec philosophers. These guys wrote about their existential angst over the impending end of the world and consequent nothingness. After all, someday they'd run out of neighbors to sacrifice and the gods would pull the plug. Somehow we've managed to produce goth and emo poets without those guys to build on, so I don't feel the loss. Crushing the Aztecs was the best thing the conquistadors ever did.
Mann wraps up the book by claiming the American tradition of liberty is derived from the Iroquois. In his telling every European colonist seems to be a devoted adherent of the feudal order. The Indians they meet did as they wished, led by chiefs who carefully avoided pissing off enough of the tribe to be overthrown. This was not new to Europe--it's how the Germanic tribes who overthrew the Roman Empire lived, and how the Celts conquered by the Romans lived.
In all these cases--Iroquois, German, and Celt--the tradition of liberty only existed in a low-population density society. It didn't survive as the tribe grew larger. From the Mississippians to Charlemagne free and easy chieftainships grew into monarchies and theocracies.
The United States managed to create sustainable personal liberty by drawing on the republican traditions of Athens, Roman, and Renaissance Italy. Mann tries to hand-wave that away. I have to wonder how much other hand-waving he's doing to inflate the historical importance of the Native American societies.
I want to like this book. It's full of fascinating information about people only mentioned in passing in my other books. But I can't trust it. So it can't be part of the home-schooling library.
EDIT: See comments for the author's response.