The Banishment was the mass exile of elven religious dissidents from the Kingdom of Eita in the middle to late third millennium. After a period of discontentment, disruption, and sometimes violent actions by elves religiously opposed to the creation of the aeroliths, the ruling scholar-nobility of Eita chose to cast out the dissenters from the Cradle, forcing them to find new homes and communities elsewhere. Most of the Banished either journeyed east, eventually settling in modern-day Talmithe, or otherwise made their way underground where they slowly transformed into the deep elves.
Background
The construction of the aeroliths, while hailed by most in Eitan society, was not looked upon favorably by all. A small yet prominent group within Eita saw the the flying cities not as a sign of hope and development, but rather as a grave risk against all mortal life. Acquiring the skymetal asteroids for the aeroliths required reaching beyond Kishar into the blackness where there was no air. To some elves, doing so was believed to attract the attention of Voltumna and Urusthe, two of their most evil gods who reside in the void. Extending their grasp too far was therefore an existential threat, as it ran the risk that the gods or their underlings would see the elves' activities and react with anger or in some other incomprehensible way that could doubtless only lead to ruin. They could only guess at what the consequences would be. Perhaps they would be met with divine retribution or visited by a great calamity. Either way, they were confident that only devastation could follow in the footsteps of their hubris.
As the efforts to build the aeroliths intensified, so too did its opposition. Impassioned debate in the scholar-halls turned to protests, then to disruption and sabotage of incomplete aeroliths, then finally to violence targeting the aerotheurges and engineers who designed the flying cities.
Banishment
By the middle of the third millennium, it had become clear to the Eitan ruling class that they could not allow the discontentment to continue. Those who were known or suspected to harbor dissenting views were cast out of Eitan society, forced to wander the world in search of places to establish new communities far away from the Cradle. The exact date or even year of the Banishment has been lost to history. Eitan scholars intentionally struck such details from their records, along with any information about who precisely was exiled, and the Banished themselves chose to forget in order to create a hard break with their old civilization, which they viewed as now irredeemable.
Aftermath
Though some traveled the world, eventually setting down roots in all manner of new places, most of the Banished either made their way east to the lands that are now Talmithe, or else went underground instead. In Talmithe they eventually formed the modern tribes, or houses, that now rule the region. The Talmithen elves have never forgotten their origins, but in the many thousands of years since the Banishment and later the collapse of Eita have largely softened their religious views somewhat, as their worst fears did not come to pass - at least, not yet.
The Banished that journeyed to the Darklands did so out of a belief that if Voltumna and Urusthe were to shifts their attentions from the voidto Kishar, the safest possible place to be would be as far underground and away from space as possible. Over the years they found themselves changed, both culturally and biologically. Life in the Darklands, especially in the regions under the Sangora Desolation where most settled, is a far cry from the almost utopian abundance they had previously enjoyed on the Cradle. Their societies became increasingly callous and cruel as those once allied turned against each other in competition for scarce resources. At the same time, over several generations their forms and appearances began to shift, as they evolved pale, almost translucent skin, developed dark sight and extreme light sensitivity, eventually turning into modern deep elves.