The "Great War" was a massive conflict that took place during the Void Century. It was fought between the Great Kingdom and the Alliance of Twenty Kingdoms. The cause of the war is unknown, but according to Vegapunk, it was a clash of two competing ideologies.[1][2]
The war took place between 900–800 years ago. For yet unknown reasons, twenty monarchs came together and formed the Alliance to fight against Joy Boy and the powerful and advanced Great Kingdom. The Ancient Weapons were used during the battle, and as a result of their destructive power, the sea level rose by 200 meters. This caused the former continents of the world to sink beneath the ocean and left behind only scattered, disconnected islands. In the end, Joy Boy was defeated by the Alliance and the war came to an end.[1]
The victorious Alliance went on to form the World Government and began to systematically erase records of the war and the Great Kingdom, resulting in the so-called "Void Century". Research into the Void Century and the Poneglyphs was forbidden with the justification that it could enable the revival of the Ancient Weapons.[2]
800 years after the Great war, Dr. Vegapunk learned about the war after studying texts left in the wake of the Ohara Incident. He then created a recording that would tell the whole world about the war, which then activated upon his death. He also stated that the war never really ended, as its legacy continues to affect the world in the present.[1]
Beasts Pirates(Legendary Hour, Fire Festival, New Onigashima Project)*
Blackbeard Pirates(Duel on Banaro Island, Summit War of Marineford, Payback War)*
Straw Hat Pirates(Operation Utopia, Davy Back Fight, Buster Call, Celestial Dragon Hit-and-Run Incident, Operation SOP, Dead End Race, Turtle Car Race, Pirates Festival)*
