"The World Until Yesterday" is Jared Diamond's third book in the trilogy that includes "Guns, Germs, and Steel" and "Collapse", both of which which I enjoyed slightly more than this latest one.
The TL;DR summary is that human civilization is only about 10,000 years old, but humanity itself was thriving nicely for several million years before that in a very different world, one without governments, without literacy, without obesity. And he thinks modern humans can learn something from our former way of life, which he explains by looking at modern primitive societies like those of Papua New Guinea, whose people were still using stone tools and living in complete isolation from the rest of humanity in 1930 but today have internet and airports.
He acknowledges that the lifestyles of these tribes are in some ways brutal. They are more vulnerable to sickness and violence than modern city dwellers, for example, but on the other hand they have never heard of diabetes or heart disease. They just don't get fat. I thought that the the MMM forum's strong paleo crowd might appreciate his discussion of why that is. (Hint: you won't be surprised to learn that modern humans eat a lot of things our bodies don't want.)
He also talks about the way these societies treat their elderly, how they raise their children, how they settle disputes, and how they wage wars. In most cases, he thinks primitive societies do these things better than modern societies.
The first book in the triology was about why European civilization grew to colonize the world, rather than Africans or Native Americans. The second was about how major civilizations of the past have failed and disappeared. This one is about how civilizations change over time, for better or worse, when they grow enough to support bureaucrats and politicians. As such, I think it has slightly less sweeping conclusions. The first two books say something important about humanity, and will change the way you see the world. The third is an interesting afterthought, but not quite so life changing.