Every long-running fandom has its grail question, and ours has been sitting in plain sight since the '90s. An entire civilization, the most technologically and philosophically advanced people Tamriel ever produced, stopped existing between one heartbeat and the next. The series has never answered for it. Morrowind took us to ground zero, handed us eyewitnesses and primary sources, then smiled like Vivec and told us nothing definitive at all.
What makes the mystery genuinely good rather than merely unsolved is that we know the when with absurd precision. 1E 700, the Battle of Red Mountain. Kagrenac, Chief Tonal Architect, turns his tools on the Heart of Lorkhan, and every Dwemer in the world vanishes. Not just the ones under the volcano. The Rourken exiles away in Hammerfell, the clans of Skyrim and High Rock, all of them, in the same instant. Any theory worth holding has to explain that synchronization. Most casual answers can't.
So let's rank what the sources actually support, strongest first.
1. Kagrenac and the Heart: the only near-certainty
Every account that matters agrees on the mechanism. Yagrum Bagarn, the last living Dwemer, bloated with corprus in Divayth Fyr's Corprusarium and trundling about on a centurion-spider chassis, believes Kagrenac's tools are responsible, though he was off in the Outer Realms when it happened and came home to an empty world. Vivec, who was actually on the mountain, gives the Nerevarine the same mechanism from the other side: Kagrenac used his tools on the Heart, and the Dwemer were gone. Where the two split is the outcome. Yagrum fears Kagrenac destroyed the race outright; Vivec admits he doesn't know whether the experiment failed catastrophically or succeeded perfectly.
And the Dwemer knew the stakes, because they argued about them in print. The Egg of Time is untranslatable to us, but Yagrum summarizes it: Bthuand Mzahnch's rebuttal of the position that tapping the Heart's power was an unjustifiable risk. Nobody publishes a rebuttal unless someone serious is arguing the opposite. Put it beside "Divine Metaphysics", which (again per Yagrum) sketches how his people meant to use the Heart and Kagrenac's tones to build a new god, and you get a civilization holding a live safety debate right up until someone ran the experiment. They weren't ambushed by fate. They pushed the button themselves.
That's the bedrock. Everything below is an interpretation of what the button did.
2. The Brass God: they became the skin of Anumidium
Declared bias: this is my favorite, and I'll defend it at the end. Baladas Demnevanni, the Telvanni recluse holed up in Arvs-Drelen doing actual archaeology while the Temple recites doctrine, works through the Dwemer texts and lands somewhere startling: the disappearance and Numidium are the same event. In his reading, Kagrenac wasn't destroying his people, and he wasn't evacuating them either. He was installing them. Binding the whole race into the Brass God as its substance, its skin, the animating stuff of a deity built rather than born.
What sells it for me is the downstream weirdness it quietly explains. Numidium does not behave like a very large centurion. At the Warp in the West it behaved like a hole in causality, collapsing Daggerfall's endings into contradictory outcomes that all happened. Machines don't do that. Gods barely do.
3. The calling
Buried in Morrowind's dialogue is a stranger notion: that the Dwemer heard a "calling" and followed it out of the world. As a theory it's frustratingly mechanism-free: no source says who called, or from where. But it has two odd points in its favor. Yagrum survived precisely because he was standing in an Outer Realm, which proves "outside the world" is somewhere a Dwemer can physically be. And Radac Stungnthumz, the ghost down in Bamz-Amschend in Tribunal, was already dead when it happened, and stayed. Whatever took the Dwemer had rules. It took the living and left the dead, which sounds less like an explosion and more like a summons.
4. The zero-sum reading
The most metaphysical answer, adjacent to all the CHIM talk: the Dwemer (militant skeptics who refused worship as a category) collectively achieved the inverse of CHIM, denying the Dream so completely and so unanimously that the Dreamer stopped dreaming them. The in-game evidence is tone rather than testimony. "Hanging Gardens of Wasten Coridale" survives for us only in fragments, and what little can be read mostly demonstrates how alien Dwemer thought was even to the Altmer trying to parse it; their books resist translation the way the people resisted belief. I'll be straight with you, though: the strongest statements of this idea live in out-of-game developer writings, not on any bookshelf in Tamriel. Gorgeous theory. Thin sourcing. Rank it accordingly.
One aside for the news-minded, since every TES 6 hype cycle drags the Dwemer out of mothballs. The latest round of supposed leaks pointed at Hammerfell, and the press flagged them as likely fabrication, so treat all of it as rumour; nothing about the setting is confirmed. Still, if the game ever does land there, that's Rourken country, Volenfell and the ruins of Stros M'Kai, and this question stops being academic.
Where I land
I promised to commit, so: the Brass God. Baladas's reading is the only one that actually explains the synchronization, a single tonal operation on a single artifact re-binding a race that had spent centuries building instruments for exactly that kind of work. And Numidium's later career, a construct that breaks time itself when switched on, reads far more like something running on the soul of an entire stubborn species than like a machine waiting for soul-gem fuel.
So here's what I want argued in the replies, and not gently. Yagrum stood closer to the Egg of Time debate than anyone alive and still can't tell us whether Mzahnch won the argument; Vivec watched the whole thing happen and won't say what he saw. Whose silence do you weight more heavily: the engineer who missed the moment, or the god who didn't? If you've got dialogue lines or book passages I've underplayed, bring them. That's what lore and theories is for.
If you enjoyed this, the lore desk also has a piece on the Towers and one on who Talos really is.