Around 2976 SD, four centuries before the present, every dragon-bond in Adron was cut in a single working. The order that did it kept its fortress at Waterdark, hidden in the Gozwin Mountains, and worked two elements together that few master at once: water and darkness. They killed no dragons. Killing a dragon was unthinkable in Adron then as now. They severed the bond instead, and that alone was enough to end the Wyrmward and the world the riders had built on it.
The reason Adron keeps is that the bonds had begun to sour. The dark leyline runs through the center of the kingdom, and along it the soul-deep coupling between rider and dragon had started to bleed in a direction no one had a name for. Riders sickened in ways no healer could read. Dragons turned strange, then turned away. The order's account, the one Adron has held to for four hundred years, is that they cut the bonds to stop the souring before it took every rider in the realm. By that telling the Severing was a mercy and a rescue, however much it cost.
What it cost was the kingdom's whole order of power. The dragons, their bonds gone, scattered to the wild or simply left; the riders were riders no longer; and the houses that had served the caste rose into the empty space and became the banking kingdom that rules from Adrak today. A severed bond is not a clean cut, either. A bond has a shadow-half, and shadow loosed from a living thing goes to Malstaris, the gray plane under the Wastes where the shadows of the dead are gathered. The Severing sent the shadow-half of every rider's and every dragon's bond across in one stroke. What that quantity of severed shadow did once it arrived is not a question Adron asks aloud.
Waterdark, the night of the working. No army at the gate, no fire on the walls. Across the whole of Adron, in the same hour, riders woke with a cold weight gone out of them and could not say what they had lost until they reached for the other mind and found nothing reaching back. By morning the dragons were gone from the Drakespine. The watchtowers have stood empty since.
The order survived the Severing and still keeps Waterdark, quieter now and far smaller. The faction within it that took the blame did not survive. They were cast out of Adron entirely, and that expulsion is remembered now as the Megélren Exile.