The Reign of Dragons was deep time, ten million years and more before the calendar, and it had already ended long before the Shattering — other races walked into the world, and the dragons that had ruled it became one power among many. Then Hykravones broke Nagatayora open in the sky, and the dragon-father's death thinned what was left. Through the early Modern Era dragons were scarce in the settled lands. They kept to the deep ranges and the drowned coasts, far from the rebuilding peoples, few enough that a generation could grow up having never seen one. By 8,104 BSD that was no longer true.
Nagayeshi never stopped. The cone at the eye of Oblivion went on warming its buried clutches through the whole long recovery, Eyatora went on raising what hatched, and grown dragons went on leaving across the sea the way they always had, indifferent to whether the world outside still remembered them. The Shattering had killed the dragon-father and scattered his kind; it never touched the hatch-ground. So the Return was not an invasion mounted from anywhere. It was arithmetic. A hatch-ground that outlived the catastrophe put more dragons into the air each century than the one before, until there were again enough abroad to be felt, and a world that had learned to do without them met them with fire. The middle centuries of the Great Expansion were bloody for it.
The returnees never shared a purpose, whatever the later chronicles made of them. Rothogomos cracked a dwarven kingdom open for its gold and has brooded over the corpse ever since; Kanzekill barely notices the realms in her shadow, lost in a four-century hunt of her own. Off the Blades, Chavux raids the strait shipping and Adron will not raise a hand, because one law binds the whole kind without regard to temperament: no dragon may be killed, conqueror and recluse alike. That a raiding dragon is sacrosanct is the Return's longest-running consequence, and the one a strait full of robbed merchants would most like to see ended. Shoryaven gave more of his fourteen-volume Chronicle to the Return than to any other upheaval of the age, and read it as the hinge on which human dominion turned.