In the Year of Blue Fire (1385 DR), a magical disaster called the Spellplague changed the face of Toril (the land of Forgotten Realms), its lost sibling Abeir, and even the planes themselves. Flesh, stone, magic, space, and perhaps even the flow of time were infected and changed.
Most scholars believe that the Spellplague was the direct result of the murder of the goddess Mystra at the hands of Cyric, which Shar engineered. This popular theory holds that magic was bound so long in Mystra’s Weave that, when the goddess died, it spontaneously and ruinously burst its bonds. Areas of wild magic, already outside the constraints of the Weave, touched off first, but the plague raged on and on in ever-widening spirals, devastating some places and leaving others untouched. It even tore through the realms of demons, gods, and lost souls before the end.
Ancient realms that had passed beyond easy reach of the world were pulled back, such as the Feywild (called Faerie in ancient days). The Abyss, home of demons, fell through the planes, unleashing swarming evil before finding its new home at the bottom of the Elemental Chaos. Even the long-forgotten sibling world Abeir burned in the plague of magic, despite having been cut off from Toril for tens of millennia. Portions of Abeir’s landscape were transposed with areas of Toril in the disaster. Such landscapes included their living populations, bringing realms such as Akanûl and Tymanther to Faerûn’s face. Across the Trackless Sea, an entire continent of the lost world reappeared.
The Spellplague was a potent agent of change, but it also set off a whole string of secondary catastrophes.