Holy War「聖戦 Seisen」was a huge conflict that took place 3,000 years ago between the Demon Clan and the Stigma alliance of the Goddess Clan, Fairy Clan, Giant Clan, and humans. It serves as a catalyst for most of the series.
Over 3,000 years ago, the Goddess Clan and Demon Clan constantly clashed with each other, but due to both being so powerfully equal, they sustained a balance of power among the five races. Eventually that balance was broken when Meliodas, the leader of the Demon Clan's Ten Commandments and the Demon King's eldest son, betrayed his clan by killing two members of the Ten Commandments and fled with his lover, the Goddess Elizabeth.
This moment of weakness among the Demon Clan gave a huge opening for the Goddesses, and took the opportunity to ally with the other races and strike against the demons, starting the Holy War. While most of the war is unknown, thousands from all of the clans lost their lives in the war.
Nearing the end of the war, Meliodas and Elizabeth's parents were fed up with their children's betrayal against their clans and punished them by killing them and giving them each a unique curse. The Supreme Deity punished Meliodas with a curse that would cause him to stop aging and bring him back to life and devour his emotions every time he dies without fail, while the Demon King cursed Elizabeth by making her reincarnate as a human and every time she dies she would forget all memories of her past lives, and if she were to regain all memories of her past lives, she would inevitably die three days later in front of Meliodas.
How the war ended is not explained, but it is revealed to have happened during the time between Meliodas' first death and resurrection: the outcome being the Demon Clan having been sealed away in a ritual done through the Coffin of Eternal Darkness, bringing peace to Britannia for the next 3,000 years. The Goddess Clan sacrificed their physical forms to seal away the demons and their souls came to inhabit the material found in Britannia, while the giants and fairies withdrew to their own realms, leaving the humans as the dominant race in Britannia, causing them to spread and populate the land and dividing themselves into different kingdoms. It was stated by Ludociel that the Goddesses had to seal the Demons after their strongest warrior, Mael of the Four Archangels, was slain by Estarossa of the Ten Commandments but the truth was that Gowther had manipulated the Goddesses to end the Holy War by, with help from his doll, using a forbidden spell that would sacrifice his life in the process. The spell altered everyone's memories of Mael - even the gods themselves - by thinking he was killed by the Demon King's supposed middle son Estarossa, whom Mael would take on that persona.
New Holy War Edit
3,000 years after the original war, the Ten Commandments were freed from the Goddesses' seal and began wreaking havoc among Britannia and soon were able to take over the majority of the land. After Meliodas reveals the truth behind his and Elizabeth's past, Elizabeth's memories are returned by Zeldris and the curse her mother placed on her begins to take effect. During this time, the Seven Deadly Sins plan to take back the kingdom of Camelot from the Demon Clan, but the Ten Commandments place a trap, ultimately forcing Meliodas to revert back to his original self.
As this occurs, the Goddesses begin to take the physical forms of Humans to serve as vessels for their disembodied souls. The former leader of Stigma: Ludociel, possesses Margaret's body along with his fellow Goddesses: Sariel and Tarmiel. They meet up with Elizabeth and the Sins, except Meliodas, Ban, and Gowther, back in Liones, where Ludociel makes an agreement with Elizabeth and the Sins to reform the Stigma Alliance to fight the Demon Clan and start a second Holy War.
The war involved a lot of battles between the allied forces and the forces of the Demon Clan. Liones is defended by several of the Holy Knights that formed the "Defensive Force". The Fairy King's Forest is defended by the armies of the Fairy and Giant Clan, who later join the "Search-and-Destroy Force" to fight the largest troops of the demon army.
Estarossa of the Ten Commandments who is later revealed to be Mael of the Four Archangels, is consumed by the power of the Commandments that he had absorbed and is confronted by several of the Seven Deadly Sins, Elizabeth Liones, two of the Four Archangels and Derieri; the last three being killed in the course of the battle. Mael is finally defeated by the Fairy King and returned to his former self by Gowther, expelling the Commandments from his body.
With Camelot completely taken over after the death of Arthur Pendragon, the "Assault Force" is directly confronted with the headwaters of the Demon Clan: Zeldris, Cusack and Chandler. After a hard battle, the two major demons decide to merge in their true form, the Original Demon. To make matters worse, the five Commandments that were free, meet to be absorbed by Meliodas, who already had in his possession the other five and was in the process of becoming the new Demon King.
The Assault Force looks unconscionable while Escanor is defeated by the Original Demon and Merlin is immobilized to carry out the Chrono Coffin that will hang the cocoon of Meliodas in time before becoming the Demon King. However, with the help of the Sins, Elizabeth and Mael, Zeldris and the Original Demon are finally defeated and the Chrono Coffin is completed.
However, Meliodas emerges from the cocoon before the time was suspended, revealing himself as the new vessel of the Demon King. The Sins and Arcangles try to fight, but the Demon King proves to be too powerful. That's when Ban, who had successfully returned from Purgatory, appears to face the Demon King, along with the emotions of Meliodas, who fought against the Demon King in the spiritual world. After joining all the Sins, the Demon King is finally defeated and Meliodas regains his body.
With the defeat of the Demon King, the remaining troops of the Demon Clan retreat from Britannia, officially ending the Holy War.