Editing Eberron (section)

===The Day of Mourning===
One afternoon in mid-994, Cyre just... went up in a giant ball of mist.

Cyre was fighting a Breland-Thrane combined force for the past few days, near the town of Making (where there may have been some unusual research going on by House Cannith, Cyre, or both).  The Cyrans were actually doing pretty good: they fought well against superior numbers and held ground to bring up reinforcements.

On the afternoon of the second day, after they had fought to a standstill, that's when everything went to shit. A grey mist started emerging from the royal palace of Cyre, moving to cover the capital city and, within the day the entirety of Cyre. Those caught in the mist the first day died instantly, but those who entered the second day onward merely have difficulty healing within the mists in some places. Most buildings remain intact, but some have been turned 90 degrees or found miles away. Making has become a giant, eternal, lava sprout which cools into an obsidian mountain that keeps growing bigger. The mist stands to this day, cleanly marking the former borders of Cyre. Indeed, the mists end so cleanly at the end of Cyre's land that a port city's docks are outside of the mists which led to several of the survivors. Inside the mists, the dead don't decay and in some places healing spells nor natural healing works on those not born within the Mournlands. Spells also came alive, literally, turning into a new type of creature called a [[Living Spell]].  Think about all these shitty spell combos you ever came up with on an optimization forum somewhere.  Now take that awful combo and make it a creature that doesn't age, eat, or sleep, and just continually attacks things on repeat until destroyed or otherwise subdued. But it wasn't just the living spells that were created that fucked things up.  A massive number of its citizens just died, crops withered to nothing, and all sorts of terrible mutations came about as a result of whatever rampant madness claimed the nation. Even years after that event, the land refuses to grow and any life that inhabits it suffers from the land sucking away any life.  Corpses that died on the Day of Mourning still lie there, preserved by whatever awful power was unleashed.  Life practically became uninhabitable, thus any survivors of that terrible event fled and the Mournland is all that is left of that proud nation.

There is no explanation for the Day of Mourning, not even an internal one, and with current policy never will be. The borders of the Mournland matching the borders of Cyre suggests it was no random event. Popular in-universe theories are someone's weapon going wrong (or right), overuse of magic, one of the planes deciding to turn Cyre into a big ol manifest zone, and an Overlord being unsealed.  A popular out-of-universe theory is that Cyre was actually taken by the mists into the [[Demiplane of Dread]].  5th Edition's take on Ravenloft confirms that at least a small part of Cyre, a lightning rail, was taken by the mists but leaves the fate of the rest of the country up in the air.