Why does anyone get this into their head to do this? At some point Emile Zola decided that it would be a good idea to write a huge series of novels based around the interlinked tales of one family.
The whole series would take him over twenty years and finish up comprising twenty separate full sized novels. One of them, Germinal, would go on to become one of the great classic novels. It would be easy to regard the whole series as one of the all time classics of mission creep. But in the introduction to the very first one of them, the Fortune of the Rougons, Zola makes it clear that the large scale of the project was something that he conceived from the very beginning.
The Fortune of the Rougons is a book that is seeped in the history of the time in which it is set. But Zola never writes about politics. He writes about people's reaction to politics. The events of French history play a key role in the book, but the book is about the way people's lives play out. What he is particularly good at is handling the way that politics motivates people. It is rarely straight forward. We get to realise why the characters take particular sides. And how their own motives shape the way they see and react to events. For example, having brothers as political opponents is a good plot device, but the way Zola sets it up is completely believable.
The background in history is that of the sudden collapse of the second French republic and its replacement by a new empire under Napoleon III. The Bourbons had been overthrown in the revolution of 1848. The republic that came in after this was a bit shaky from the start. It lasted only three years before being replaced by, of all things, a second go at an empire under Napoleon III.
Social divisions in France at this time were deep and bitter and were reflected in political divisions. It is the genius of Zola that he can weave all this into a novel which also has deep human interest as well. The innocent love affair that takes up much of the middle of the book is beautifully described and oh so believable, but has nothing whatever to do with the bigger picture. It brings home that even at a time of great political and historical drama, on the ground ordinary people have to continue to live their lives and that really that is the real thing that is going on. Reading this book is a great way to get a feel for the history of this period in France. But you learn a great deal more as well.