DM: You find a [Obviously plot-related item]. It is stamped with a symbol. The symbol looks like [Describes a symbol].
Raven: Okay, can I roll-
Other Player 1: Oh, God! It's the [Whatever] of [Something or Someone]!
Other Player 2: Oh, ****. Maybe it's not real. Maybe it's actually the [Huh?] of [Character I've never heard of].
DM: Yeah, like I'd give you guys THAT!
Other Player 1: Yeah, if it were that, then [Very long string of events that either will happen or could or did or whatever...]
Other Player 3: No, you're forgetting about [Obscure piece of lore that means that one little thing in the above speculation couldn't happen].
Other Player 2: Yeah, it would be like that time when [Recites seven-and-a-half minute recap of specific Warhammer history].
Other Player 1: Yeah, and then [Picks up where Other Player 2 left off and goes on for another four minutes].
Other Player 2: I bet [Really Obscure Character] would love [or hate, whatever] that!
Everyone laughs except Raven and Other Player 4, who also knows nothing about Warhammer Lore.
DM: So, where were we?
Raven: I was asking if I could roll a History check to see if I would know this symbol.
DM: Oh, right. No. It's too obscure.
Raven: Great.

Once upon a time, the world was a pretty nice place. This is when the Lizardmen, or at least their froggy bosses and mythical makers, were the only folks worth writing home about. The mythical makers moved continents around and uplifted the other sapient species, but the lizards were where it was at. Then somebody screwed up and the poles became gates to hell. Nobody liked that. Except probably mortal mages since magic comes from there too.

The elves and dwarves do stuff initially as allies but then they decide to piss each other off. Elf Mordred eventually turns evil just like mom, and his BS ends up doing a half-Numenor to the elf homeland and splitting his people philosophically, resulting in the current flavors of elves.

After that, humans really show up with the rise of Fake Egypt Land. It's pretty nice until a scheming evil wizard takes charge. He gets run off. Then Egypt invents vampires. They get run off. Eventually that scheming evil wizard (now lich and necromancer) does a big animate dead spell which basically swarms egypt with all their dead, including every king who ever reigned, so egypt is skeleton land now. The necromancer gets beaten up but he keeps coming back like a good lich does. Seriously, he always comes back.

People faff about fighting each other in conflicts that don't add much to the grand scheme of things until the germanic human tribes unite into an empire, lead by a guy called Sigmar. He's pretty important.

Sigmar spends most of his life going around beating up all the assorted baddies of the world that he can reach. There keep being new ones, though, what with people making demon pacts and all. After ruling for fifty years Sigmar wanders off and the Empire becomes the elective monarchy we know and love, and also starts worshipping the dude as their new god.

For the next 2500 or so years, little changes the status quo but that it changes back. Most governments get more centralized and tech advances at an absolute snail's pace. but what you see is mostly a refinement of what things were like in the Sigmar days.

So you've got the Empire. They're the Holy Roman Empire with some early-steampunk-ish tech at the far end. They really like their first emperor, Sigmar, and their current(?) emperor Karl Franz is pretty good too. They're also a fractious bunch of loons who fight each other almost as much as they fight external enemies, and who have some technically distinct provinces in terms of culture, like Kislev being kinda Russia.

Joining them in the human corner you have Bretonnia, which is King Arthur myths. They worship the Lady of the Lake and love poncy knights who are awesome because it turns out that strange women living in ponds and distributing swords and magical blessings is a great system of government.

There are other humans, most notably Cathay (China) but they never got armies so how important could they possibly be?

The Lizardmen are still around, but they mostly have this "primitive" May-inca-tec feel, sort of like the River Heralds in Ixalan, despite being the scions of the original and most advanced sapient race.

Speaking of still around, Elves come in three flavors. High elves live on their fixer-upper Valinor and are all things shiny and proud. Dark Elves live in Canada and are basically the Cult of Rakdos with extra slavery except they follow Elf Mordred, Malekith, and his mommy Morathi, instead of a big demon. Wood Elves live in discount Lothlorien, conveinent to Bretonnia, and do all the spooky fey wild hunt stuff.

We've also got Dwarves, or as Warhammer calls them, Dwarfs. They are every dwarf stereotype ever. People love them because of that, not in spite of it.

There are also Chaos Dwarfs. Like anything with capital-C "Chaos" in their name they're corrupted by hell powers. Since Dwarfs aren't exactly Magic compatible this is a little weird for them and they have a really cool magitech volcanic Babylon vibe that simultaneously goes against the Dwarf grain and yet feels very in character for when the hidebound rockheads turn evil. But their army was short-lived, unloved, and unsupported so how important could they possibly be?

Undead come in two main flavors: the Tomb Kings, who are skeleton Egypt, and the Vampire Counts who despite owing their existence to Egyptian diaspora are perfectly Hammer Horror Transylvanian. Seriously, their territory is called Sylvania and their biggest badass is Count Vlad. Not subtle.

The Greenskins, aka Orcs & Goblins are around everywhere pretty much acting as agents of small-c chaos. They're a mistake of the uplift program that the Lizardmen and their creators never managed to exterminate and they pretty much party and pillage as an unpredictable vector of conflict. The joke is they talk in cockney-style slang and aren't very bright but somehow they still manage crazy inventions that naturally malfunction about as often as they work, usually explosively.

Few people care about the Ogre Kingdoms. They live on the edge of the map (which is to say between fake Europe and Cathay) and while they have some extremely vague mongol stylings, their thing is mostly that they're hungry. But they had a supported army, so they must be important.

Then we get into the Chaos Crew. First up, Beasts of Chaos, aka Beastmen. They're vaguely Chaos-affiliated tribal Satyr people who are big and buff and pretty much get called upon when a rampaging horde more grimdark and less funny and charming than the Greenskins is needed. But they had a supported army, so they must be important.

Next up, Warriors of Chaos. They're vaguely nordic demon cultists, for whom valhalla is becoming one of the demons they worship to fight eternal, edgy and grimdark. They're sort of a philosophical buffer state between the rest of the world and the real demons that are largely stuck on the wrong side of the polar portal, so you can fight Chaos without having to go toe-to-toe with the actual big bads, thus keeping said big bads threatening. Their boss is Archaeon, who managed to be chosen by all four of the demon gods, which is a pretty big deal seeing as the four demon gods hate each other more than they hate anything else. He's kind of the front and center big bad of the setting.

Finally from that group Daemons of Chaos. They're demons. There are four chaos gods who rule over them and every(some exceptions apply) daemon is aligned with one of the four like daemon Hogwarts. Khorne is big and red and likes fighting. He is the blood god per Blood for the blood god!. There's a fan theory that the four chaos gods represent different sides of the fandom, and Khorne would be the pure wargamers who just want their plastic mans to do smash -- the timmies, if you please. Tzeentch is the god of magic and trickery and timey wimey schemes and his daemons are all weird colors and do magic and maybe have bird traits because Skekses are cool. If you buy the gamer thing, Tzeentch represents the strategists who come up with detailed plans and love to pull them off and outthink everybody -- the Johnnies of the warhammer world. Slaanesh is the god of pleasure, and its daemons would probably have the succubus/incubus vibe if there wasn't a real effort to keep them disturbing and freaky. Still, they're somebody's fetish. The gamer archetype here is the painters and hobbiests who are obsessed with looks. Then there's Nurgle -- Grandfather Nurgle or Papa Nurgle as he's called. He's kind of the god of life, but Nurgle loves all life including microbes so he's more the god of disease and rot than anything else, so his Daemons all do poison stuff. Still usually protrayed as both the most friendly and the most toxic thing in the universe simultaneously. He represents the gamers who don't know how to bathe.

And then there are the Skaven, a group of rat people who, like House Dimir, supposedly don't exist as far as most of the world is concerned. They're impossibly numerous, merciless slavers (mostly of their own kind), and mad scientists that the Phyrexians would really love, since their various clans do diseases, monster-making bio science, insane magitech, and then there are the odd group out that are ninjas. They love the number 13 and have their own god, the Great Horned Rat, who eventually became a fifth Chaos God on par with the big four (or above Slaanesh, who got imprisoned in the AoS lore) and believes in secrets, backstabbing, and ruthless evolutionary progress along with bizarre uncontrolled magic and arcane tech. yeah, remind you of anyone?