The Great War (大戦, Taisen), also known at The Eternal War, was a war between all races that began so far in the past that nobody remembers clearly and ended about six thousand years ago.
During the war, the sky was bleached red and falling blue ash-like particles covered the land. These were said to be the remains of dead spirits, and were highly poisonous to any part of any living body it came contact with. The world seemed to have been much colder, although still warm enough for humans to survive. It was most likely heated by the surrounding ashes upon the ground since the sun hadn't been seen for thousands of years.
The war was caused by the gods, also known as Old Deus, to obtain the Star Cup, which has the power to do anything and thus the wielder will be crowned the Only God or the True God. The participating Old Deus in the war had their creations fight for them; excluding the Ex-Machina and Holou. The attacks of the stronger races frequently transformed the landscape. Much less animals lived during this time. Humans could only survive by living secretly in caves and sending scouts to scavenge the wreckage left from battles between other races.
The war was won by Tet by default in the end, and after Tet claimed the Star Cup, he forbid all violence and thus created the Ten Pledges. He also completely morphed the world of Disboard from the bleached red skies and the remains of dead Elementals to the colorful vibrant world it currently is. With the introduction of the Ten Pledges and him being the God of Play, every conflict was decided upon by games from people's lives and national borders. The "final goal" of Disboard is to unite all of the 16 sentient races together and challenge him to a game for the position of One True God.
- Judging by Azriel's age, the war most likely lasted for around 40,000 years.