I bought this book in 1999, based on Bill Gates' incredibly concise and informative review, and ironically finished it between jobs.
This book changed my perspective on history, and provoked a curiosity for understanding linguistics, history, prehistory, agriculture, the evolution of technology, the cultures of tribes, etc. all of which have still not abated. Criticism that the book is very repetitive is not justified in my opinion, because Diamond packs so much information into it.
The book is an answer to a question by a Yali, an aboriginal native of Papua New Guinea, as to why different cultures and countries are so unequal, if there are no basic biological differences between the races. Jared Diamond's hypothesis is that it is geography, nor race, that determined the fates of human societies. He distinguishes between proximate causes (like steel weapons, immunity to diseases, organized armies) and ultimate causes (like domesticable plants and animals, coastlines, topography) which led to the undeniable differences among cultures or nations.
He lays out the situation on various continents - not just the prehistory of Mankind, but that of the flora and fauna on various continents, in the first chapter. Not just the major clashes - Europe versus Inca - but even the minor but illuminating ones - Maori versus Moriori - are discussed, with telling effect.
Then Diamond develops his thesis in the next six chapters, quite elaborately. His last five chapters, a tour de force of Africa, China, Polynesia etc are marvelous summations of their histories, and the forces that shaped them. I suggest searching for and reading Bill Gates' review to get a grasp on this book. And strongly recommend this book.