Human beings cooperate in their millions, a scale of sociability only equalled by some of the social insects - but those are highly interrelated. So two questions: how did large-scale societies emerge from small-scale hunter-gatherer groups in the not-so-distant past; and how were genetically-diverse humans able to make such a transition at all? Here is a brief and highly-oversimplified summary of Peter Turchin’s answer to the first question, the main concern of his book.
Compared to the dominance hierarchies of chimpanzees and gorillas, human hunter-gatherer groups are much more egalitarian. This is the basis for enhanced cooperation, necessary for cooperative hunting and defence against large predators. Around 11,000 years ago, however, there was a turn to agriculture, first seen in the middle-east.
Agrarian societies, even early, small-scale ones are not viewed with admiration by hunter-gatherers. They are inegalitarian and bad news for the overwhelming majority. Even the concept of private ownership of lands and crops is anathema to the HG mindset. Most likely it was the improved productivity of agriculture in the presence of constant conflict which led to the first war-leader ‘upstarts’ establishing a durable hold on power.
The first ‘archaic states’ arose in southern Mesopotamia and south-western Iran around 6,000 years ago. These were led by ‘upstarts’ who had successfully legitimised their on-going rule by self-deification, the ‘God-Kings’. Archaic states were bloodthirsty, used extensive human sacrifice and oppressed their subordinate groups who lived in constant fear.
Between 800 and 200 BCE we see the Axial Age, the period of great (and less internally blood-thirsty) empires. Despotism doesn’t scale well, particularly amongst multiple ethnic groups. Great Religions became the glue (Confucianism and Taoism, Buddhism, Judaism, Jainism, Zoroastrianism, Greek Religion/Philosophy all developed around this time). The empire’s rules became decoupled from the person of the ruler, and a theological egalitarianism bound diverse ‘citizens/subjects’ together.
So again, why the transition? The new driver of change was the arrival of the steppe nomads, with their highly mobile cavalry and composite bows - so effective that defence required a further increase in agrarian state size – only empires could defend themselves. The empires themselves now became strong enough to engage in expansionary offensives against other states in winner-take-all conflicts.
The new great religions helped to pacify relationships within the empire, increasing both internal political stability and the cooperation which permits economies of scale. And in an important sense, that has been the historical story to the present day.
This account is grossly unfair to Turchin’s detailed argumentation founded upon his encyclopaedic knowledge and sharp insights into fundamental causal mechanisms. The author is a key leader of the ‘cliodynamics’ movement which seeks to give a mathematical expression to historical evolution; the material in this book is underpinned by computer simulations of the onset of the Axial Age as explained in his 2013 PNAS paper ‘War, space, and the evolution of Old World complex societies’ (available as a PDF online and worth reading - h/t Razib Khan).
There is a gene-culture coevolution story waiting to be told here – recent work in population genetics based on historical genomes suggests significant plasticity over the time periods of interest in this book. Most likely this has some causal input into why certain transitions took thousands of years: it seems unlikely that it merely took that long to come up with the required new ideas.
In summary, Peter Turchin has written a gripping, original, thought-provoking book which offers a new way of thinking about human history: it is highly recommended.