Nonfiction Worldbuilding Inspiration for RPGs Public

As an addendum to my RPG Worldbuilding Tools List, I want to create a list with nonfiction works that can be used as inspiration for RPG worldbuilding (or the building of fictional worlds in general). Some guidelines on what I am looking for:

• They should not be primarily RPG books - that's what the other list is for!
• Books that give good overviews how societies, cultures, and technology work can all be useful. However, the goal is to assist with worldbuilding and bringing fictional works alive instead of "Do-It-Yourself" books. For instance, a book on how bread has shaped cultures and trade might be useful, while a book on bread recipes probably isn't.
• They should have a fairly large scope, and not be about one very specialized subject that would only be useful to a very small number of RPG settings.
• They should not be written in High Academic, but be reasonably accessible to interested laypeople.
• Pure works of fiction themselves do not qualify. However, "guidebooks" to fictional worlds and settings can qualify as long as they don't limit themselves to one particular fictional universe.

If you have any suggestions, please tag me with @juergen_hubert@bookrastinating.com and give me a short explanation for why you think a particular book would be a worthwhile inclusion.