The Calamity referred to a connected series of cataclysmic plane-wide events across the Feywild in the opening decades of Quelmar’s CR Era. They'd completely redefine the realm and the faefolk who inhabited it for the coming centuries.
History
Prior to the Fracturing of the Weave, the Feywild was the source of many of the chaotic magics accessible to the Material Plane. The connection between the two planes was essential for the flow of arcane energy, and when that connection was severed the build up of this power had catastrophic and far-reaching effects on the fae realm.
The Sundering
The most visible change was the sundering of the land itself. Entire regions would be destroyed, created, or changed. Dramatic landscapes formed: mountains launched into the air to become floating islands, giant mushroom forests sprouting up overnight, a stylish apartment complex forming out of the ocean's water, entire cities wiped out. For many years the land would remain volatile and changing; nomadic fae became an ever increasing sight across the realm, whether displaced from their homes, or merely from the curiosity of experiencing this new world.
The Court Wars
It wasn't only the landscape that would be destroyed however. Delicate diplomatic treaties that had maintained the balance of power for eons would seemingly become meaningless. Violent conflicts would arise between the fae courts as resources were suddenly scarce and abundant across the continents. The fiercest fighting unsurprisingly came between the Seelie, and their long time rivals the Unseelie. The Unseelie saw their opportunity to dethrone the most powerful of fae courts -in an attempt to claim their demi-god like status for themselves- causing the only recorded plane-wide war in the Feywild. The Court Wars roped many of the smaller fae courts into the opposing factions as the two staged proxy wars amongst their own fronts.
Incursion of the Feydark
The fighting came to an uneasy truce with the appearance of the Feydark. The sundering ground caused a devastating tear through the Vesian Plains, revealing passageways to the Feydark - the Wild’s equivalent of The Underdark. It wasn’t long before hordes of horrific, twisted, arcane-infused fungal creatures spilled forth from the passages and brought further death and destruction to the Feywilds. The courts were forced to cease hostilities in order to face off against the mindless mycelial swarms as their corruptive presence poisoned the land. As the spores spread, infected animals and faefolk would succumb to the rot and become one with the swarms, turning against their own kind. It was unknown if some unseen hand was guiding the monsters from the depths of the Feydark’s twisting labyrinth of tunnels, however the invasion was finally halted after a group of heroes descended in. Whilst the adventurers were never to return, the tunnels were sealed and the corruption receded.
Following the incredible loss of life, the courts were not eager to rekindle their direct conflicts in their weakened states. A cold war formed between the two factions, which had become much more evenly matched in terms of their strength and influence. Small skirmishes would pop up from time to time, but espionage was the more prevalent front.
Magic
The use of magic during this period and beyond became substantially more dangerous and risky, on top of powerful. Surges of wild arcane energy became increasingly commonplace, causing a huge range of unpredictable results. Some communities eventually outlawed the use of magic except in times of great emergency, whereas some opted to try dispel the arcane energies from regions entirely as an act of defence.