Keyblade War

The Keyblade War (キーブレード戦争) was a mysterious conflict in which many Keyblade wielders fought prior to the events of Kingdom Hearts Birth by Sleep. According to Xehanort's research, the conflict arose when the people created Keyblades to obtain the χ-blade and, with it, control Kingdom Hearts. This results with the Keyblade users fighting among themselves in a war that drastically caused the Kingdom Hearts universe to be remade into what it is today and shattered the χ-blade into seven pure lights and thirteen pure darknesses. The conflict also resulted in the scarred remnants, littered with fallen warriors' Keyblades, that would someday be known as the Keyblade Graveyard. The survivors resolve to use the Keyblade to protect the worlds soon after while the Keyblade War eventually faded into legend, becoming a fairy tale told in Radiant Garden. The story also came to Atlantica, with King Triton initially treated keyblade users with contempt before meeting Sora..

Several years later, a Keyblade Master named Xehanort researched the Keyblade War and decided to unlock the mysteries of what took place at the Keyblade War's end through creating the χ-blade and causing another Keyblade War. In a move he would admit was sloppy on his part, Xehanort intended to recreate the weapon by joining two hearts, one of pure light and the other of pure darkness. The chance presented itself when he purged his former apprentice Ventus of his darkness and created Vanitas, then having the two be at equal strength before having them rejoin to create the χ-blade. However, the union was imperfect and χ-blade became unstable. Despite the set back, Xehanort was not deterred from his course of action.

As a secondary plan, Ansem, Seeker of Darkness, prior to obtaining Riku's body as a vessel, travels back in time and meets with Master Xehanort's younger self, sending him on a mission to create an organization of thirteen different incarnations of Xehanort, or thirteen darknesses for Master Xehanort to pit against seven lights as an alternate way of recreating the χ-blade and starting another Keyblade War. The new Organization XIII comes to include Master Xehanort, Young Xehanort, Ansem, Xemnas, Xigbar, Saïx and six more hooded figures. Master Xehanort's plan to make Sora into the final vessel for his essence is foiled when Riku, Mickey, Lea, Donald and Goofy intervene, and the twelve current members disappear, returning to their proper points in time for the time being.