The Crack in the Sky

There was a summer when the skies above the Ten Thousand Spires turned red. The seas went still as glass, and people all across the archipelago found themselves looking to the northwest, as though their attention caught by some sound just on the edge of their hearing.
Expeditionary boats and skyfoils were sent by the Collective, but gossip travels faster than mechanized sails, and they received the news en route from curious merchants and fisherfolk: the entire island of Verhuren had disappeared.
By the time the Collective's fleet arrived in the sector and the diviners set up their augurs to figure out what was going on, the sky and sea had returned to normal. There was a ring of flotsam and people, living and dead, about a mile offshore from where Verhuren had been. The island itself, its cities and spires and harbors and people, was simply gone, as if none of it had ever been there.
Survivors, plucked from the ocean clinging to makeshift rafts or the flaming wrecks of skyfoils, later described seeing a fissure rip open the air above Verhuren, spewing fire and ash and the singing of eerie angelic voices.

Well, we were just two miles out when the main starboard foil caught fire for no damn reason. All of us yelling and cursing and trying to right the ship when that singing started. Quiet-like, and it seemed like the whole world shut itself up just to listen. I swear to you, we stood there listening and not a one of us did a damn thing until we hit the water, and even then it was just to grab something floating so we could keep right on listening. I'd have walked into fire to hear more of that music. I guess a lotta people did.
--Jakob Havelaar, captain of the skyfoil Brandende

I was swimming in open water one time, and a whole pod of whales breached maybe twenty yards away from me. Something that size breaks the surface, you can feel it, goes right through your body. It was like that, I guess. Like something real big that had been over there was now right here.
--Jan Verbeek, fisherman

The Dvebl kingdom was no more. Dwarves living in other nations were seized and questioned ruthlessly; the authorities of the Collective interrogated diplomats and scholars, engineers and navigators, and a large smattering of random people with no connection whatsoever to politics or magic. It was a time driven by panic and paranoia, with desperate suspicion and persecution heaped on the Dvebl already rocked by the loss of their homeland.
The official report from the Collective was that the Dvebl had been conducting secret military research for several years. Dubbed Project VOC, it was the brainchild of Willem Vogel, at the time richter of the Dvebl kingdom. Vogel, a brilliant legal mind and prodigious conjurer, had a scheme to simultaneously strike pacts with three great infernal powers (Valefar, Oriax, and Crocell). The idea, it seems, was to exploit tenuous treaties between these extraplanar beings, ensuring favorable, loophole-filled contracts for the Dvebl and guaranteeing an overwhelming military advantage against the other nations in the Collective.
Needless to say, something went horrendously wrong; but perhaps most alarming to the fact-finders of the Collective, no one was able to figure out exactly what. Dvebl wizards were already considered significantly more advanced than other schools in the fields of interplanar bindings and travel. Of course, essentially all of their best minds were involved in Project VOC, and had thus perished or vanished. The numerous attempts to scry on Verhuren or its inhabitants met with failure, and the efforts at actual interplanar excursions fewer and fatal. After the complete debacle of the Panjang Expedition, further efforts at locating Verhuren were forbidden. The Collective outlawed interplanar travel and pact magic, and, eventually, an unsettled new equilibrium was reached.
The Crack in the Sky changed Klissidar forever. The six nations of the Collective are now only five, and while the tensions that had long simmered between them didn't really go away, the current unspoken agreement is that the expansionist magical warfare of generations past has simply become too dangerous. The organization of the Watching Eye was created as a pan-Collective monitoring body, ensuring that the bans on pact magic are enforced and that no under-the-table magical research is going to rip open the cosmos again. The nations turned inward, clamping down within their own borders, squeezing money, magic, and technological secrets from their own people.
In practice, of course, the jockeying for supremacy amongst the Collective's nations has simply moved battlefields. Real power now is not just about technological or magical advantage, but political influence and information. Governmental agents and private interests alike are constantly looking to suborn officers and tech emplacements of the Watching Eye, which is now almost completely composed of various partisan splinter groups. Anyone who claims to represent the good of the whole Collective is almost certainly lying.
Of course, not everyone accepts the official narrative of what caused the Crack in the Sky. One common theory is that one or several of the Collective's nations destroyed Verhuren with their own secret magical superweapon, blamed the Dvebl for it, and used the ensuring chaos to seize authoritarian power. Some believe it was retributive action by the old powers or the gods; others that it was simply something that happened for no reason at all. Now, generations later, most people in Klissidar don't really think about the Crack in the Sky, except that it was definitely the fault of the warlocks, or the dwarves, or whatever group the person in question already dislikes.