Netheril

The Netheril Empire were intruders on our plane, humans who were forever altered by the magic that saturated their realm as well as the intense magics they had routinely used over many generations. They were involved in a war with another civilisation – a war in which they prevailed but the magical fallout caused their home to be wracked by magical storms and events that made it unhabitable.

They created a magical bridge called the Crossing Shrine that connected their plane to another, one where they could begin anew, where they would face no challengers and could reign supreme – the plane Malador, where The Realm resides.

The Netheril kept a protected outpost within their home realm and the Crossing Shrine active for two reasons: Netheril who, for whatever reason, were not born on their home plane were normal humans and were outcast – leading to the barbarian tribes that would eventually form The Realm.
 * so that newborn Netheril could be born there (a 'trueborn' Netheril needed to be born on their homeplane The Realmand be saturated in their plane's powers)
 * so that they could periodically return to bathe again in the magical energies of their plane – to not do would eventually lead a Netheril unable to perform magic and eventually wither and die.

However the Crossing Shrine, by way of it's construction, impinged upon Malador's elemental Plane of Air and Al'akir, the Primordial of Air, was displeased. His anger over this intrusion built over the centuries before he led an attack of air elementals against the Crossing Shrine, irreparably critically damaging it.

The Netheril were faced with an awful decision – stay on Malador and slowly wither and die or return to their all but destroyed home plane. They chose the latter. Many died as they hurried over the crumbling magical bridge or were scourged by wild magics as the small outpost could not hold them all. They eked out a pitiful existence in a single city grown from that outpost, their powerful magics enabling survival only by the barest of margins. Al'akir and his legions of elementals guarded against any further construction. And so the centuries passed, until the events of A Bridge between Worlds.