When the 5e Dungeon Master's Guide DMG came out back in 2014, I read it from cover to cover. I knew I'd be running games, so I needed to know about the rules of the world. That is, of course, what the DMG is. It contains the rules for things that aren't the player characters themselves, but that inherently effect player characters. I was a little underwhelmed when I first read through the book. I was there for useful tables, secret magic items, and those are the sections I use today, but my memory of the rest of the book is section after section of advice on how to build a D&D-compliant world and design adventures. I've decided to re-read the 5e DMG, though, to re-discover anything I impatiently overlooked on my first read-through, and I'm going to review it chapter by chapter.
It identifies the actual purpose of the book early:
This book, the Player's Handbook, and the Monster Manual present the default assumptions for how the worlds of D&D work.
Yes, this is a book that "reverse engineers" how a D&D setting is built.
The first chapter covers gods, settlements, magic, calendar systems, currency, and finally the campaign. It's full of context for existing adventures, and even more ideas for creating your own.
What stands out the most for me are the details. There are so many minor details you might throw in to your game world that you may not have thought about otherwise. For instance, I almost always refer to gold pieces as gold pieces. Who doesn't? Well, how easy is it to acclimate your players to terminology like "nobles" for gold pieces and "ravens" for silver? You don't even have to tell players what it means. They'll catch on when an NPC says "I'll give you 50 nobles to go fetch the MacGuffin" and then hands them a bag of 50 gold pieces. It's trivially easy immersion. And this chapter is full of little tricks and tips like that.
There are a few tables hidden away in the chapter, including a really nice Starting equipment table you'll never find when you need it.
This section of the DMG hints, I think, at the way the 5e designers thought the game would work. For instance, there's a section on Factions, and as I read it, I had the smallest notion that Factions maybe were expected to be integrated into forthcoming adventures more than maybe they were in the end. This is all speculation, but in the early adventure Princes of the Apocalypse, Factions are mentioned a lot, and several NPCs in the town of Red Larch are identified by the factions they belong to. I haven't read all the 5e adventures (yet!) but I don't see (or at least, I don't recall) that emphasis on factions in, for instance, Out of the Abyss or Tomb of Annihilation.
Pathfinder has used factions since its beginning. In fact, the name of the game comes from the Pathfinder Society, a social group that exists both in game and in the real world. The in-game Pathfinder Society is a faction of adventurers, and the real world Pathfinder Society is a system of organized Pathfinder play. In the game, there are many other factions with goals and political interests that are sometimes in concert and sometimes in conflict with one another.
It makes me wonder whether factions had been something the 5e designers had intended to be more prominent. Of course, Guildmaster's Guide to Ravnica actually does use factions (in the form of guilds) and the better part of the book is spent establishing what each faction is about. I've said in a previous post that Ravnica made me see how factions could actually be a workable replacement for alignment, so the idea of factions being used as a central mechanic appeals to me.
And then there are ideals, bonds, and flaws. I can't remember now how often they're mentioned in Chapter 1 but they come up several times throughout the book (as I write this, I'm roughly half way through.) As a DM, I've used ideals and bonds some, but I've never felt that players actually care about them. As a player, I usually don't even bother generatingt them. I don't really get what the 5e designers had in mind for the ideals/bonds/flaws system, and the DMG sheds no light on it. There are no rules provided in the DMG for what ideals/bonds/flaws actually means to the game, to the DM, or to the player. As far as I can tell, it's purely for flavour. I remember it being used explicitly and mechanically as a form of detrimental madness in Out of the Abyss, but otherwise it seems to be rarely mentioned in any substantial way. It very much feels that ideals/bonds/flaws are what everyone complains about alignment, all over again.
I wish there was some rule that made ideals and bonds and flaws matter. I don't really understand what the designers are trying to achieve with them, but I could imagine a system in which you earn an epic boon (that's later in the DMG) if you met a condition listed in your bond, or maybe you have to make a saving throw to fight against a demon trying to steal your soul (no more resurrection for you) if you do something that invokes your flaw, or whatever. I wonder, as with the factions, whether the designers had something clearer in mind with ideals/bonds/flaws, and it just never got borne out in subsequent adventures.
It's fascinating what an in-depth analysis of a simulated reality reveals about our own world. The DMG describes every component of the game as if though they were exclusively fictional elements. It asks you to imagine a world in which there are towns, economies, wars, religion, multiple languages, factions of groups with differing interests, and so much more. Well, it's obviously not hard to imagine that, because that actually describes our reality, and yet by holding them up as if though they were imaginary, and looking at all the potential ways you could make them look in your own fantasy world, you do start to see some of the scaffolding that maybe was meant to be hidden. Imagine designing a world religion, for example, that's monotheistic. It might sound strange that anyone would believe that just one god could or should manage all metaphysical domains, but in a fantasy world anything is possible. Imagine an economy based on arbitrary metals that are mostly considered valuable only because they're relatively rare and difficult to unearth. In real life, obviously, that would never happen because people would see the inherent lack of value of, say, gold over something more pragmatic, but in a fantasy world anything is possible.
The list of examples goes on and on. Maybe that was the hidden truth within D&D that nobody wanted to be revealed. Maybe the actual Satanic Panic was (and is) the idea that you can examine reality with the aim to change default assumptions, and to improve the system to be better for everyone.
This is a book in which the maintainers of D&D tell you explicitly, in excruciating detail, how to do their job. The D&D DMG has always been that way, all the way back to 1st Edition, but I feel that most past editions have focused more on technical specifications than on worldbuilding. This one very clearly prioritises how to create a D&D world that fits the mechanics of the game.
I do sincerely believe this book is atrociously organised, though, so I recommend downloading my list of tables to help you find the information you need as a quick reference during a game.