I believe the Bible to be the word of God. That doesn't mean I believe the Earth came into existence on Sunday, October 23, 4004 BC (James Ussher, 1650) or that it is only 6,000 years old (Martin Luther). Instead, I believe the creation account in Genesis to be more allegorical than literal when it speaks of ‘days.’ The Bible, after all, wasn't written as a modern-day history book for a scientifically-sophisticated audience, but as a religious book. Nonetheless, I do believe the Bible literally in many respects. I believe there was an Adam and Eve; I believe the Earth was completely flooded in the time of Noah; and I believe Jesus was born of a virgin and is the literal son of God. I do not know exactly how all these things happened but I have faith that there is a rational explanation which will satisfy science and religion. I have faith that science is revealing many truths, but I also have faith in my religious beliefs based on personal experiences that are difficult to explain to someone without similar experiences.
First of all, he flatly rejects racist claims of superiority based on skin color or race. Instead he argues that geography and biogeography played a central role in creating the modern-day haves and have-nots. While Diamond briefly goes back to the beginnings of human development and explains its spread out of Africa, the book is mostly about explaining why some groups made the leap from nomadic hunter-gatherer to sedentary (stay in one place) farming cultures. Such a change allowed for larger populations, better nutrition, and advances in agriculture and crop and animal domestication.
And domesticated crops and animals is a big factor in why modern civilization has its origins in Eurasia. The area known as the Fertile Crescent had more wild plants and animals available for domestication than anywhere else. Domesticated animals also provided labor that drove further advances and gave advantages in war (especially the horse). These factors contributed to centralized governments and written languages and ever larger concentrations of people. But it was this combination of high density cities and domestic animals that created the most effective tool of conquest: germs.
(As a side note, I found the chapter about language especially interesting. He says written languages have arisen independently only in a few places, and one was in Mesoamerica – Mexico and Central America – around 600 BC. Readers of The Book of Mormon won't find that date surprising, nor will they think it "independent.")
It's hard to summarize such a far-reaching and encompassing book like this, but it does a good job of explaining the grand scope of history understandably. This is not to say it's an "easy" read, however, as it required a careful reading. It's also not without detractors, and a few online reviews had very technical complaints. I'm no expert in such history, although I was a little bothered by the tone of the book sometimes. He disparages "white racists" – and rightly so – who claim racial superiority but he pushes the opposite too far and occasionally engages in his own subtle racism. When he talks of the spread of white Europeans in the Americas he uses words like "kill" and "infect" but when he discusses the spread of Bantus in Africa he uses words like "expand" and "engulf," and then downplays the word "engulf" with a lengthy paragraph softening it. There were a few times I thought his logic was weak and evidence thin, like when he claims New Guinea natives are smarter than Europeans but cites only his opinion as evidence. Still, I found it to be an interesting and enlightening book, and it gave me a lot to think about.