Time and History (Voidhaven Supplement)
From D&D Wiki
There are four main eras in which a campaign might be set, though you are free to elaborate/fantasise differently. The world which came to be known as Voidhaven was peopled only by the ancients, until they summoned chaos itself.
Portals opened all over the world, spitting forth humans, orcs, elves, dwarves, and more, closing again at some unknown command. The portals increased in frequency and size for many years, and each race had to fend for themselves as they explored the new world.
This chaotic time was the Age of Clans. It came to a close as the most powerful of the spellcasters among the newcomers realized the danger and sealed the portals. The void was close now, but could not consume this new home.
Each civilization settled into a home and society began to flourish. Magic use was widespread and almost worshipped because they had saved creation itself. This was the imperial age, known such because the humans built an empire which spanned much of the mainland, trading with other nations.
The clockwork age changed how magic was seen. Technology could produce similar results to magic, but it was not reserved for those who were devout, or studios, or simply born to it. Anyone could take part, and magic began to be shunned.
When forbidden magic was mixed with Clockwork, the warforged were born, and the gods trembled. Countless demons were summoned and consumed to power the new war machines. The reply of the gods was to retreat from the plane, bringing all magic with them. Voidhaven began supplying her own life force in order to endow the races with magic, defying the gods. Thus began the Apocalypse as Voidhaven began to die.