I think you're letting the fact guide your idea of the narrative of history a bit. Just as one example, the anti-war protests during Vietnam were another massive example of social unrest, and that didn't happen on a 50 year cycle.

I tend to think any cyclical view of history is inherently not accounting for many things that don't fit into its narrative.

You might not be as crazy as you think. I really enjoyed The Fourth Turning, which posits generational cycles in history. "They substantiate their hypothesis by identifying and tracing a repetitive, four-stage historical cycle that, throughout recorded time, started on a high note and ended in hardship."

I think some of their predictions fall flat since the book was published, but it's interesting to think about: the "engine of history" is the child generation reacting to the parent generation.