I recommend The Dictator's Handbook for ideas on how to run any domain where the PCs are rulers. It proposes a theory of power called Selectorate Theory, which posits that the only difference between autocrats and democrats is the size of the winning coalition required to stay in power, and what a leader has to do to keep them happy, that is, to make sure they are rewarded.
The Dictator's Handbook by Bruce Bueno de Mesquita and Alastair Smith
The Little Ice Age by Brian Fagan - insightful/informative book about the role climate change has played in human civilization