This book was written in the 1990s, and its authors seek to explain a pattern in American history, where crises seem to occur about every 80 years, followed by a spiritual revival in the interim. The author focuses on what he sees as types of generations, some more civic and outward-motivated, others more spiritual and inward-directed, and how these types replay over time and interact with the various crises and spiritual revivals that occur. The best part of the book was the amount of research the author did, particularly into pre-20th century America, where there are most likely limited records, to support his theory. He also explains how generations don't change that much as they get older, so some generations are more rebellious, while others are more conservative (but we tend to think of young people as rebels and older people as conservative, although this is not always true). He explains how generations have differing impacts as they make their way through the lifecycle.
The author predicts a crisis around 2020, and there have certainly been many problems, although I can't see anything that really matches earlier crises (Revolutionary War, Civil War, World War II). Had the coup attempt in January 2021 succeeded, it would fit the bill, but it's failure, and the political failure of most of its supporters have made that possibility more remote. If Putin's attack on Ukraine had succeeded, that also might have provoked such a crisis, but again the failure doesn't really work. The pandemic and political polarization certainly are problems, but I can't see either one as a crisis on the same level. So, I would take the author's predictions with a grain of salt, although I think the book is a worthwhile read.