I really don't buy the Fourth Turning thing.
World War 1 doesn't count and a financial crisis every 10-15 years going back 200+ years only counts when it lines up with their 80-year cycle.
The most turbulent period of recent American history was the 1960s, not the 1940s.
I think instead philosophical ideas trickles down through other fields and shape human behavior. The Dark Ages and Renaissance weren't 80-year cycles. Ultimately many particular factors combine to create specific events.