I do not have this book at present, thus I can only write what I remember.
Overall I would say that anyone interested in history, particularly milleniarism, should read/buy "The Great Year." The book is an engaging, comprehensive survery of milleniarism along with a great deal of history to boot.
"The Great Year" and "The Great Week" are views of history that have been accepted by many cultures/religions - Hebrews, Christians, Platonists, etc. According to this view, history is predetermined and fulfills itself in phases of various lengths. In the Hebrew book of Jubilees a "year" is 49 years, for example. In another culture a 4-phase historical cycle may involve completely different time scales. The Hebrews tended to see their "Great Year" cycles as successive renewals with God's covenant through prophets like Moses, with alternating cycles where the covenant is broken and people suffer, the explanation given as not following God's laws. Everyone is certainly familiar with how Christians believe their destiny will be fulfilled!
The author of "The Great Year" argues that history is not predetermined, that human behavior and events are not so predictable, and that historians often bias their accounts using various filters, especially the theory that history and humanity are always progressing.
Very broadly speaking, what the author seeks to accomplish in this very large survey are three things: 1) To define "The Great Year" concept and pinpoint how and when it manifested itself in various cultures. Millenarian movements in Christianity and other cultures are discussed thoroughly. Some readers may be surprised at how widespread and pervasive milleniarism has been over time in many cultures and religions. 2) To show that historians who view history in terms of progress are in error. Karl Popper wrote a book called "The Poverty of Historicism" that Campion and others have cited to show that historical accounts are often biased by false preconceptions. 3) To demonstrate that a number of currents in history, such as Marxism, are actually millenarian movements themselves, describing history in their own terms of fulfillment of their predetermined goals.
I feel that the author suceeds very well with these aims. I was particularly impressed with his insight in observing that adherents of the more modern movements such as Marxism and Nazism indeed act exactly like those who claim that a select group of people will be "saved" because they believe in a "Saviour," that history is following their version of a predetermined conclusion.
In the end, however, I found parts of this otherwise excellent book unsatisfactory because the author, while accurately depicting the fallacies of other historical views, himself falls into what I would call the trap of reason, that reason and material "proof" are the sole arbiters of "truth."
In the first part of the book Mr. Campion critisizes Jung for the latter's writings which stated that excessive materialism had corrupted mankind and made it more bellicose, hence 2 world wars in an era of great technological progress. He claims that there is no "proof." It's a shame that Dr. Jung can't defend himself, as I'm certain he could. But let me say, if the lack of spiritual values - compassion, tolerance, humility, a bond with something Divine, etc., which have in no way kept up with our material development in this century - is not one of the major causes of our almost total preoccupation with materialism, then we might as well discard the timeless teachings of many teachers, theologians, and others, who have attempted to bring some civility and purpose into this often Godless, corrupted world. Personally I am not willing to do this.
I also found the author's attack on "New Age" thinkers, like Helen Blavatsky and others, only too typical of the trite criticisms of materialistic thinkers. I even checked out one of his sources, who wrote a trilogy debunking Blavatsky and others (I can't remember the author's name), and parts of the 2 books I perused were in my opinion sadly failed attempts to attack the messangers while not attempting to take on the far more difficult and important task of evaluating their messages. Not at all surprising, for how can we "prove" that there is a God, or that there are Masters of Wisdom, karma, reincarnation, etc., which would point to some spiritual meaning for life? There are those who try to prove these things, even doctors, scientists, etc., but from what I could tell from this book, to Mr. Campion and his sources it's doubtful that any proof would ever suffice. To me a purely materialistic reading of history, where there is no ultimate Purpose and meaning - which I would claim can be pursued by trying to grow spiritually, often through multiple physical incarnations - is itself in one important sense lacking in purpose.