No one appears to know what caused the Minor Cataclysm (or if they know, they’ve kept it secret). It appears to have begun with rippling waves of light and energy coursing over Adnati. These ripples came in pulses that filled every hour of the day and night. These pulses slowly decreased day by day, month by month, until they finally disappeared entirely more than a year after they started.
Ultimately, the waves appeared to have been largely benign, though a few things of note occurred. During this year, sorcerers of Wild Magic triggered surges with virtually every spell cast, large or small. And babies who had been gestating during this period were invariably found to have some sort of innate magical abilities, though their abilities were not always strong and were not always passed along to their descendants.
Though scholars understood very little about the Minor Cataclysm, they chose to use it as the mark of the end of the Fifth Age and the start of the Sixth, the present age. As it is currently the year 3121, is has been three millennia since the Minor Cataclysm occurred.