The Sundering

In the fifth century before 0~IA~, the trials of Malat-ir against the dark god Naarel ended with the wizard creating the Sundering, a planar region containing only the world of Gradia and small shards of the surrounding planes of existence. Notably, the astral plane was completely cut off - magical effects that involve the astral must instead use another plane, usually the shadow plane.

Magic

Another effect that the Sundering created was that the power and abundance of magic in Gradia faded, dwindling to a tiny fraction of what it was within only a decade. The Pilvevium is like a closed system; no new magical energy enters from the outer planes of existance.

Magic has not completely disappeared from the world, however. But where once magic had permeated everywhere, only a handful of natural sources remain. Magic still works, but great works of magic now require a way to draw from one of these natural sources.

Elven Peoples

The Einir and Alfir, being tied to another plane and drawing much of their essence from it, dwindled in both power and number once the world was split from the other planes. Whereas beforehand all elven peoples were nearly immortal and had at least some connection with magic, the split cut off their innate magic and reduced elven lifespans down to a couple centuries at best.

Different groups reacted differently to this sudden change. In the south, the vast empire of the Alfir crumbled into balkanized fiefdoms within a decade, and within a few centuries the Alfir lands were only a small fraction of their former size. The Alfir became far more xenophobic and returned to a simpler life and eventually to a more tribal social structure.

In the north, the great Einir kingdom of Eindonallan had a slightly more stable descent. Its population still dwindled, but the Einir, already highly focused on academics, turned to wizardry to help bolster their waning innate magics. Even the power of wizardry was waning, however, and by the time of 0~IA~, Eindonallan was merely a city-state where there once had been a great kingdom. The Einir used what remaining magic they could to hide their city away, and recede from the outside world.