Basically the book attempts to answer the question:
"Why did different societies on earth develop in such different manners?"
Why is it that Spanish conquistadors sailed to South America and colonised the natives, as opposed to the South Americans coming to Spain?
The usual answers to these types of questions invoke a number a factors, reflected in the title of the book; 'guns, germs and steel'. But Diamond argues that these are merly proximate causes, and only pushes the question a step back rather than actually answering it. The real question then becomes why were these
societies, as opposed to these
societies, the ones who develeoped technology, complex political structures, etc. We need to look for the ultimate causes rather than the proximate ones.
Diamond finds the ultimate answers in biogeography. He argues that the ultimate reasons for the differences in socital development lie in differences in local flora and fauna, differences in terrain, differences in climate and so on.
Isn't it enough to see that a garden is beautiful without having to believe that there are fairies at the bottom of it too?
-Douglas Adams, Last Chance To See