Ibn Khaldun

Ibn Khaldun's Muqaddimah (1377) explains why dynasties rise and fall in a few generations. The key is asabiyya, group solidarity: hardy outsiders bound by kinship and shared purpose conquer settled cities, then grow comfortable, rely on paid troops and luxury, lose cohesion and are overthrown in turn. The concept travels well to parties, firms and movements. He also noticed that raising tax rates can reduce revenue, an observation later economists rediscovered.