As I'm delving into the Fourth Turning, I'm piqued by the idea of how their theory overlaps or jives with similar historical cyclic theories like Secular Cycles. Bigger span theories like Ian Morris ought to fit in to some of these, though Morris' data may not be granular enough to show it. Similarly one has to wonder with increasing technology, do these cycles speed up over time?

• Turchin, Peter, and Sergey A. Nefedov. 2009. Secular Cycles. 1st ed. Princeton University Press. https://press.princeton.edu/books/hardcover/9780691136967/secular-cycles (September 30, 2026).
• Review: https://www.lesswrong.com/posts/2weRdcvqANDq3zdPH/book-review-secular-cycles