Kitab al Ibar!
Fabulous explanation of how dynasties are formed, maintained and eventually replaced by new ones and
in the mean time, civilizations flourish!
Moreover, Ibn Khaldun provides a classical account of the difference between different communities and why they are different, their virtues and good qualities along with an account of
historical distortion of different traditions that have reached us and how to check their authenticity along with a golden formula which in my opinion is the theme of the book that one can use to distinguish between right and wrong historical narrations that reach us every now and then.
All this done by a man over 600 years ago shows how lacking we as human race have been in making use of rational work present amongst us directly related to our social and material life.