There were two Great Diffusions which had the effect of all magic and magical devices, whether mechanical or enchanted, to disperse into the atmosphere with the hope that evil magic would vanish forever. Most wizards and mages lost their powers in the process.
The First Great Diffusion
The first Great Diffusion in 1247 GUE, caused the end of the Second Age of Magic.
Good Wizards, Clerics, Mages and Witches
Evil forces hoped they could retrieve the magic and revive it, so they sent a spy to find out what was going to happen to all magic. The good wizards built a Wall of Illusion and told the spy they would hide all magic behind it.
Instead, they dispersed all magic and all magical artifacts to the atmosphere with the hope that evil magic would be vanished forever. The GUE would be free of all magic for the first time. As a result to this all the wizards were left powerless and eventually died of old age. Canuk and Wizard Trembyle were the only survivors of The Great Diffusion due to a Long Life Spell they cast upon themselves (a game of Survivor was made in their honor). For more than three hundred years it was believed that evil had vanished, and that the Great Diffusion had been a success. Until the Cluster appeared in 1620 GUE.
The Second Great Diffusion
The Second Great Diffusion was another attempt to destroy all evil magic. This time it was done by the nameless Sweepstakes Winner in 1647 GUE. Which happened sometime around the 21st of Mumberbur and abruptly ended the Third Age of Magic.