Black Spell

The black spell was released when Syris, the father of Mithris of Daeris, found King Leechian, the (at the time) current king of Belegar, and killed him. He did this because he believed that Leechian as possessed by Maegamarth. When Leechian was killed, black energy filled the lands, killing almost everyone in Belegaria, and giving Maegamarth the core of his new undead army.