Great War

The Great War (大戦) is a worldwide conflict that occurred during the Mythical Age, between the demon kingdom of Dilhade against the alliance of the human continent of Azesion, the spirit forest of Aharthern, and the divine realm of Azure Sky of the Gods. It ultimately came to an end with the Demon King Anos Voldigoad's sacrifice, who erected magical barriers to isolate the four races for a millennium so that their hatred would disappear in due time.

Two thousands years later, during the Magical Age, an attempt to restart the Great War was made by a radical group of humans led by the fallen Hero Jerga, with the aid of the Heavenly Father God Nosgalia.

Summary
The war went on for so long that the reason why they were even fighting was lost. No one knows if it was humans or demons who made the first move. But once it happened, it began a cycle of murder, revenge, retaliation, and death. Humanity, who was naturally weaker than the demon race, received support from the spirits and gods. Likewise, the demons who constantly fought one another banded together against their common foe.