Joseph Tainter’s explanation for why complex societies collapse in one sentence: the collapse of a society is a response to declining marginal returns on investment in complexity. Joseph Tainter’s explanation for why complex societies collapse in one sentence: the collapse of a society is a response to declining marginal returns on investment in complexity. Tainter uses ‘complexity’ pretty loosely. He’s referring to a broad set of things that include agriculture, fuel extraction, scientific research, education, and sociopolitical complexity. He notes that in any area that produces something good for a society, the lowest-hanging fruit is plucked first, and then value gets harder and harder to extract until there’s little room for improvement. States are the biggest manifestation and driver of social complexity (and I’ll talk mostly about states in the rest of the review) but he’s talking about the abstract property of a society – how large it is, how many specialized social roles it has, how many mechanisms for organizing or doing things. In Tainter’s model, states exist to solve problems. You can think of them as either solving collective social problems, like getting big irrigation systems to work (‘integration theory’), working to placate / oppress the productive populace enough that the elite can keep extracting surplus from them (‘conflict theory’). Either way, states tend to increase in complexity in order to deal with new challenges. That increased complexity imposes greater costs per capita. When the system hits some critical point on the return curve (highest point the graph below), the next stressor makes the state try to unlock the next stage of complexity, which demands more resources than the population can bear. Peasants revolt, republics break away, and the state falls apart.