Strauss–Howe generational theory

The Strauss–Howe generational theory, devised by William Strauss and Neil Howe, describes a theorized recurring generation cycle in American and Western history in which historical events are associated with recurring generational personas called archetypes. Each generational persona unleashes a new era (called a "turning") lasting around 21 years, in which a new social, political, and economic climate ("mood") exists.

Source: Wikipedia — Strauss–Howe generational theory (CC BY-SA 4.0)