A book to read immediately after Guns Germs and Steel is Why Nations Fail by Daron Acemoglu.
It's also useful to know that Diamond does not have a degree in Geography and many geographers aren't particularly on board with his ideas.
I think of him the same way I do Malcom Gladwell, a good story teller but he does this by cherrypicking anecdotes more than by a robust assessment of reality.
