Hello, I see this thread as one of the most useful for astrologers. I want to introduce you a book by a slovak scientist E. Pales. I'm a beginner astrologer and it helped me to understand a lot. In fact, I'd never get to know astrology and other spiritual basics without this book.
I basically recommend this book to everyone, not only to astrologers. It's name is Angelology of History (in english yet available only in a shortened brief version called Seven Archangels: Rhythms of Inspiration in the History of Culture and Nature). This book is not only about history even thought this world can be understood best through the history. The book is about everything: about the world, the universe, the human, nations, countries, nature, history, architecture, painting, music, fashion, literature, incarnation, astrology, angels, wars and dinosaurs.
When I had decided to obtain the book and heard that the author spent like twenty years by writing it, I was asking myself how can anyone spend so much time just by working on a single book. After I had read the book I was asking myself how the hell it took him only twenty years? It contains a huge amount of information. Carefuly organized information, which add to each other. If you like finding links and you're interested in mentioned topics, it is a „must have“. Links such as why a huge number of inventions emerge in one era, one must hurry not to be overtook by other inventors. At other times during a particular decade several brilliant musicians appear in just one city or in one country where noone like them in several hundreds years before or after them. At other times wars break out throughout the whole world, the plague comes, expressionism and red colour is put into practice in art, pointed caps, shoes and masculine clothing comes into fashion, a style of flames is put into practice in architecture, people start to eat more meat and human values change in the way that the biggest honor is to be brave in a fight. And on the end of such era it is like a bell's ringing for the whole world thus there comes piece and another spirit of era comes into play. Those spirits of era (I don't know if the word „ghost“ wouldn't fit better here since english is not my first lang.), according to author's theory, don't influence only a human behavior but also influence nature (evolution of species and of all living, outbreaks of diseases, natural disasters, clima etc.). Trends in issues about which we usually think that have nothing in common appear here. These spirits of eras are something like inspirational forces, are 7 of them (archangels of 7 basic astrological planets) their eras are of the same lenght and their influences overlap. Such eras have fractal character thus the highest level era takes millions of years (on this level recognized according to the current rulling sign) and it is divided into shorter and shorter eras – the shortest have 354 and 72 years and they repeat periodically. For example: Of the same character as mentioned war era (Martial period )is the Cretaceous of Mesozoic when extreme predators evolved also dinosaurs prepared best for defence (Scorpio era).
It also states that not only historical eras have their spirits, but also each continent and nation have their own unique spirit (an elaborated knowledge of Tetrabiblos). It's for example the reason why bodily parameters change at people who have moved to an other continent. And human nations don't have only their spirits but also unique missions, e.g. a mission of jews was to create the best body possible for entry of Jesus. Jews are (or were) inspired by the same force which makes drawing in of the attention of the spirit towards matter and thus its strongly focused on physical reality (the Archangel of the Moon) – manifests itself in eras when the white colour and realism dominate in art, novels start in literature, rationalism plus empirism starts in science and foremost the materialism everywhere.
To be more precise the book is a scientific study with all neccessary requirements. Although it is written by a comprehensible language to be clear to everyone. Argumentation goes on fluently and systematicaly so it won't let you swimm in any abstract notions. The author makes conclusions regularly which are often contradicting the modern science. However, his conclusions are much more reasonable.
Furthermore he doesn't stop at discovering and describing such links, he continues on towards incarnation, life after death, angels (individual unconciousness) their superiors (collective unconciousness) and angel hierarchies, about which he speaks as they're really existing. Same in the case of demons and archdaemons. The influence of such an archdaemon is well shown and characterized in a thrilling chapter about the last Martial era of 1917-1989.
Pales' work is not publicly well know because it's a total overkill for many scientists (it can hurt the Catholic Churche too). It's also a strong incentive for society where peope aren't interested in spirituality. The evolution of the human soul and foremost the immortal spirit is the main theme of Pales' works.
It's neccesary to say that the described principles aren't author's discovery. It's an ancient wisdom and he elaborates it, proves it scientificaly by statistics and connects together many branches of sciences. He is also not the only one who works with these ideas. Such principles appear e.g. in works of R. Sheldrake.
Ideas of spiritual influences were publicly known before Darwin's theory became popular (almost at the end of Moon's rule in 1879). But before publishing his book Darwin noticed that he is well aware that all the species were created by the God and his inspirational forces so he doesn't even expect to be succesful with the theory. So the idea is not so long forgotten.
If you're interested and wanna more info feel free to ask. I also apologize for mistakes I certainly did since my english is not superb.