6 ideas
Asabiyyah is the group feeling of mutual loyalty and willingness to fight and die for one another, strongest among kin-based nomadic groups living under shared hardship. A group with superior asabiyyah can conquer settled societies and found a dynasty, because royal authority is ultimately the product of a cohesive group's capacity for collective defence and aggression.
The founding generation retains desert toughness and shared glory; the second has lived through the founding and keeps some of that cohesion but takes more power into the ruler's hands; the third knows only luxury and has lost solidarity. By the fourth generation, rulers assume their prestige is innate rather than earned, and the dynasty typically falls within about 120 years to a new group with fresh asabiyyah.
Urban comfort, specialization, and reliance on walls and hired soldiers make people dependent on others for protection, weakening courage and the bonds that made the group strong. The very prosperity a dynasty creates therefore dissolves the cohesion that produced it, so success contains the seed of decline.
Early dynasties levy low taxes on a broad base, which encourages production and yields large revenue; late dynasties, burdened by luxury spending and mercenaries, raise rates and duties. Higher rates discourage productive activity, shrinking the base and total revenue, which drives further rate increases in a self-reinforcing spiral.
Historians err by transmitting reports on the authority of their sources without asking whether the events are possible given how human societies actually work. Knowing the nature of civilisation—its demography, economics, and logistics—lets one reject reports like impossibly large armies as fabrications, making social science the critical tool for evaluating history.
The plague of 1348, which killed Ibn Khaldun's parents, swept away much of the population across East and West, emptying cities, erasing dynasties' strength, and causing institutions and cultivated land to decay. He treated it as a wholesale transformation of the world, arguing that such a break demanded a new account of conditions, as though creation had been renewed.