I've been playing historical wargaming, or at least I've been playing wargames set in a historical time on Earth. The more I played with my Roman and Egyptian armies, the more I got curious about the actual histories of these fascinating historic empires. To quench my thirst for the "lore" of these civilisations, I started looking around for history books and to be honest I've it surprisngly frustrating. It strikes me that most game source books deliver a lot of information with clear categories, and they provide very clear timelines. I don't find the same to be true of history books. In short, it seems that history text books aren't as efficient at delivering information about history as source books for tabletop RPG and wargames are, and I think they should be.
For the uninitiated, a "source book" for an RPG or a wargame is a volume containing information about the world in which the game is set. It's a relatively generic term but it's almost always a term meant to set the game's main rulebook apart. The rulebook is one book, and source books are all the other books around the game. A source book may or may not contain additional rules.
For instance, imagine a fantasy game set on a world where humans and dwarves and elves have banded together to fight a supernatural tyrant. The rulebook for that game would describe how to build a character or army, what dice to roll when, what you can do on your turn, and so on. It might also contain some basic information about the humans, elves, and dwarven societies, about the oncoming evil and its hordes, and so on. One source book for the game might contain a complete history of the dwarves: how they were created by their god, what kinds of early societies they formed, how their armies are structured, major upheavals that caused them to join forces with humans and elves, why they want to fight the evil tyrant, and so on. Other source books could be released to provide the same kind of data on the humans and elves, and still another source book could be published to introduce halflings or gnomes to the game.
As an avid tabletop gamer, I've looked through RPG source books since 5th or 6th grade. These books made it possible for me to compare imaginary monsters and imagine which one would win in a fight, and debate with friends whether chromatic or metallic or gem dragons were superiour, and so on. I could compare the battle tactics of elves and dwarves and orcs.
I did this well before I played my first tabletop game, in fact. Being a reader of lore is a uniquely "geek" hobby. It's a combination of indulging in a fictional fantasy book and doing academic research. This is what nerds love. Collating data, comparing data, making correlations between data sets, hypothesizing about how the data might interact under various conditions. An RPG or wargame source book is the codification of fictional science. It provides structure and consistency to a make-believe world so that the imaginary world is more or less the same no matter who pretends to visit it.
These source books exist for all manner of fictional worlds. There are source books for really popular properties, like Star Trek (that's the one with Spock and Kirk), Star Wars (that's the one with Luke Skywalker and Darth Vader), and Middle Earth (the setting for Tolkien's Lord of the Rings). There are source books for worlds that are maybe mostly known by gamers, like Golarion (Pathfinder), Midgard (Kobold Press), Lost Lands (Frog God), the Continent (Witcher), Thedas (Dragon Age), Hyperborea (Conan), and more. There are even source books for places intended to be real world locations, like the Innsmouth of HP Lovecraft's Cthulhu stories, the far future of Earth in many sci fi games, and various versions of Earth's past.
People pore over these books. They read the stories of the imagined history, the statistical data of militaries and wild animals and other threats, they understand the [super]nature of magical systems or the world's physics, and they look at and memorise maps.
An RPG or wargame source book usually contains a mixture of fictional history for the game world and statistics for game components. A source book might specialise in one area specifically (for example, you might buy a book detailing just the history of elves), or it might be a general work that covers a little bit of everything. In a general source book, you're often able to find things like:
Source books are often written more or less on spec, at least from the audience's point of view. A publisher doesn't know whether an audience is going to buy a source book, so the first source book for a fictional world is usually:
The initial source book for a world might not even be a literal book all its own. Instead, it might be a chapter or two included at the end of the game rulebook. Regardless of what form it takes, it usually addresses just one region of the fictional world, whether that's just one city or one continent. Within that limited scope, it usually tries to cover a little bit of everything so that you're equipped with enough of an understanding of the world that you can effectively imagine yourself as a resident of that world. Playing a character in that setting, you know what kind of activities you might get up to during a typical day, who the local government is, what you're likely to find in your home town, and what dangers inevitably lurk on the fringes of civilisation.
After that's been proven a success, another source book might be published about just one aspect of the world, or maybe another region, or it might cover an even narrower timeframe in the world's history. The possibilities are endless, and popular fictional game worlds like Golarion of Pathfinder and the Sixth World of Shadowrun have had literally tens of thousands of pages written about them over the course of several [real world] decades.
They're often organised by region, time period, and any number of categories relevant to the game. For instance, a Pathfinder book might have a chapter about Absalom. I'd expect such a chapter to identify the current year, such as 4719 Absalom Reckoning (AR) for Pathfinder 2 (at publication). Then I'd expect a history of the region leading up to the current year, with a clear timeline for each major event so I understand how distant one major event is from another, and how distant everything is from "today". This model works well, and it scales pretty well, too. The Inner Sea Guide provides detailed histories for all the major regions of Golarion, while the Core Rulebook provides just a quick overview of each region so you know enough to play in the setting.
By contrast, all I remember of history textbooks from school is that Rome gave way to the Ottoman Empire eventually, and that at some point World War I happened. For most of my life, I wouldn't have argued if somebody had told me that Helen of Troy and Cleopatra were best friends, or that Socrates and Caesar debated philosophy moments before the latter sentenced the former to death. The clearest milestone I've ever had for dating things was the birth of Jesus of Nazareth, and that only because our calendar is structured around what some people assumed must have been the approximate date of the event. Honestly, I have a hard time remembering whether 0 AD is meant to portray the birth or the death of Jesus of Nazareth, so even that marker isn't terribly useful to me.
Admittedly, fictional histories have a major advantage over real ones. Fictional histories can fill pages and timelines with events as needed. Actual history sometimes has to skip over vast chunks of time because we don't have data on it. Our real world history is confusingly populated by lots and lots of activity around things that actually have surviving written records or physical evidence, and then by vast empty centuries during which basically more of the same was probably happening.
I do wonder, though, what a history book written as if it were a game book would look like. I imagine it would be a lot more clear to me than the obligatory overviews I got in school, and a lot more readable than the academic treatises I sometimes find in libraries. I'd really like to see such a thing. For now, I've been going to the source for my historic wargames by reading Herodotus on Librivox.org.