Sorry for not being very clear with my question, I am very new to writing and the book I am working on, has to do with unrelated sections for different times in history. I am concerned about how will I connect these events to the entirety of the book and have some closure so that it doesn't feel too much like a compilation of random events.
What is the unifying factor of your book? Is it an anthology of disconnected short stories? Is it an exploration of some theme?
If you are exploring a theme,
Structure the parts to make a cohesive argument, of sorts. For example, if you are exploring the theme of love throughout history, it would make sense to structure the parts chronologically. If you are exploring mythologies, it makes sense to group by either location, or similar elements - depending on what you want to say.
If what you have is an anthology of short stories,
Consider ordering the stories to juxtapose one another. That is, rather than hitting the reader with three tragedies one after another, consider placing a lighter story after a heavy one, to give the reader a breather. Just like characters are revealed best when placed opposite a very different character who can serve as a foil, stories are revealed best when placed against stories with different elements.
Another element you'd need to consider when ordering an anthology of short stories is their relative strength: you don't want to place the "strongest" story near the beginning, as all other stories will pale compared to it. You'd want to finish strong, so the last impression your book leaves is a good and memorable one. But you don't want to start with the weakest story either, since that's the "first impression" your reader gets. If that first impression is weak, the reader might not proceed to the next stories. Particularly not if the anthology is all by the same author - in such a case, the reader might decide the author isn't really good.