In Guns,Germs,and Steel, what is Diamond's methodology?

The major methodology that Diamond employs in this book is
taking anecdotes and trying to make broader theories from those anecdotes.  This is a
way of thinking known as "inductive reasoning."

Diamond
takes a number of anecdotes about history and studies them.  By "anecdotes," I mean
events that happened in history, such as the defeat of the Moriori by the Maori.  He
then tries to construct a broad theory that accounts for all of these anecdotal
events.

Historians have to use anecdotal evidence.  They
cannot look at everything that ever happened, so they have to pick specific events just
as Diamond does.  What makes Diamond's methodology different from what many others have
tried to do is that he then uses inductive reasoning to try to arrive at overarching
laws of history that have determined the course of human
history.

Diamond's major methodology, then, is inductive
reasoning.  He takes specific historical events and tries to construct laws that would
account for those events.