The Weave

All magic depends on the Wave, an interface between casters and raw magic that is governed by Mystra, god of magic. Arcane spellcasters access the Weave directly, while divine spellcasters are granted access to it by their deities and ideals. Damage to the Weave can cause unimaginable destruction, as evidenced by the Spellplague in 1385 DR, the Year of Blue Fire.