I need to add Ibn Khaldun, from Wikipedia:
Concerning the discipline of sociology it is interesting to note that he conceived of a theory of social conflict. He developed the dichotomy of “town” versus “desert,” as well as the concept of a “generation,” and the inevitable loss of power that occurs when desert warriors conquer a city….
Ibn Khaldun’s analysis looks at how this cohesion carries groups to power but contains within itself the seeds – psychological, sociological, economic, political – of the group’s downfall, to be replaced by a new group, dynasty or empire bound by a stronger (or at least younger and more vigorous) cohesion….
Interesting also is the precursor to Marx’s labour theory of value in Ibn Khaldun’s work. Ibn Khaldun puts forward the insight that all value (profit) comes from labour as Marx was later to write. He outlines an early possibly even the earliest example of political economy. He describes the economy as being composed of value adding processes, that is labour is added to techniques and crafts and the product is sold at a higher value.