The Shift

"And Thamia set the Heavens afire; burning away the cruelty and hubris of the elves, and igniting the torches that would illuminate the path of Men, leading them to a new age." - Elves 11:34, the Gygax Compendiums, Volume VI

Historians of the world speak of a time thousands of years before the rise of humankind when the High Elves ruled the world. The High Elves exerted great influence over all life on the planet, creating and enslaving a number of races for various purposes. Their power was cemented by their mastery and ubiquitous exploitation of the magical forces that flow within Eridena.
Magic gave the High Elves power and made their lives easier and its usage became so common place that it permeated every aspect of High Elf life; tasks as simple as getting dressed in the morning were often aided, or completed entirely, by magic. Scholars at the Demenian Empire's Imperial Mage Guild, and The Grand Society of Masters in the Magi Republic both agree that magic is something of a finite resource powered by all the Natural forces on planet. These resources replenish at a consistent rate through all time as all things and all life are born, live, and die. Every thing from the lowliest beetle to the tallest tree; from the smallest fish in the rivers, to the volcanoes that give the The Boiling Sea its name. With this in mind, historians postulate that the High Elves' gross exploitation of magic wiped out Eridena's magical well.
The druids and sages say that when left to its own devices Nature always finds equilibrium with itself. When the well of all magic ran dry Eridena was pulled violently out of this equilibrium, but Nature abhors imbalance. So something was done to correct it. From here, historians disagree the exact nature of the Shift. Some believe the gods sent an avatar in the form of Thamia, the oblong, red moon to exact retribution the Elves for their hubris and to refill the well. They argue that Thamia scoured Eridena clean of the High Elves and their civilization before settling into his place beside his sister, Zenia to watch over Eridena and prevent another cataclysm like the one caused by the High Elves. Others believe that as the well ran dry the High Elves found their power waning. This inevitably led to massive rebellions and civil unrest, which ultimately led to the collapse of their civilization. Further, thousands of years of relying on magic for nearly every aspect of their lives left the High Elves woefully unprepared for a life where they to rely on their own cunning and physical abilities. Unable to rebuild their civilization, and with enemies everywhere, most of the High Elves died out. Their great citadels and cities crumbled to dust.
Whatever the true nature of the Shift its effects are still felt today, thousands of years after the fact. The High Elves exist in small, isolated pockets throughout the world, many of them no longer resembling their ancestors at all. They will never attain again attain the greatness and power their race once held over Eridena. The sun as has set on the age of the elves, and it is rising on the age of the human. Since the Shift, Humans have become the most dominant race on the planet. Their cities, culture, and influence can be felt everywhere. Humans are curious creatures, and this curiosity has led them explore every tomb, and ruin they find. This curiosity has brought them tomes, and artifacts from the High Elves. These antiquities have given the humans, and other races, to bring magic back to Eridena.
No one is quite sure when Eridena's magical well was refilled, but what is known is that it has returned in a big way. Humanity lacks the affinity for the mystical arts as typically as he High Elves did this has slowed the spread of magic in a significant way, but with the rise of organized schools of magic, and even more alarmingly: the Demenian Empire's invention of the airship, some scholars, considered alarmists by their peers, warn of another Shift, and watch the world around them change with a wary eye.