The main point of this book is that geography, and not things like race or culture, is the main factor that determines which societies have become powerful and have not. In support of this main point, there are some other major points. They include:
- Societies are powerful if they have "guns, germs, and steel."
- Societies get "guns, germs, and steel" only if they can become large, agricultural societies.
- Agriculture can develop in some areas and not in others.
- Geographical factors (like the availability of plants and animals that can be domesticated), rather than race or culture, determine which areas become agricultural and which do not.
In this way, the less important points build up to a proof (in Diamond's mind) of the main point of the book.