The book is based around the premise that the growth in scale and complexity of human societies - to today’s “ultra-societies” - is the result of inter-group military competition over a scale of many thousands of years. Somewhat contradictory, the growth of larger scale co-operation and harmony within societies has enabled them to more successfully compete militarily with other societies. Societies are defeated unless they also adopt better cultural practices to promote group trust and cooperation. Societies that cannot compete are simply wiped out, or dominated. The arguments tie in very nicely with the books by Steve Stewart Williams and Joe Heinrich that I’ve read recently on group-level cultural evolution, although neither of them considered war as the central driver of change.. It would be depressing if the result of all this is the discovery that societies go “backwards” towards less cooperation and egalitarianism in the absence of conflict. Turchin’s ultimate project is a “science of history” - a science of social and cultural evolution with the ultimate promise of practical policies that governments can enact to foster social harmony. A very thought provoking book, and very well written too. I’m keen to read some more by him now.