In ancient times, people believed that light was a gift from an unseen land by the name of Kingdom Hearts. But Kingdom Hearts was safeguarded by its counterpart, the χ-blade. Warriors vied for that precious light, thus beginning the "Keyblade War". The violent clash shattered the χ-blade into twenty pieces—seven of light and thirteen of darkness. And the only real Kingdom Hearts was swallowed by the darkness, never to surface again.Master Xehanort
The Keyblade War (最初のキーブレード戦争 Saisho no Kīburēdo Sensō?) is a legendary conflict that occurred long before the events of the Kingdom Hearts series, yet is a major driving force behind Xehanort's actions.
Both Yen Sid and Xehanort revealed that when the World was whole and full of light people desired the power of Kingdom Hearts, many creating the first Keyblades in order to obtain the means to control Kingdom Hearts: the χ-blade. However, many sides clashed over who would get the χ-blade, causing a massive war that consumed everything in darkness as the ancient weapon was shattered into twenty pieces, seven of pure light and thirteen of pure darkness, and the "true" Kingdom Hearts disappeared into the darkness.
However, the light within the hearts of children kept the darkness at bay yet separated the worlds from each other. The remnants of the battlefield on which the Keyblade War took place became the Keyblade Graveyard, littered with Keyblades of fallen warriors. The remaining Keyblade wielders resolved to protect the World from further destruction, becoming guardians of the World order.
The story of the Keyblade War was passed into legend, and the Keyblade was depicted both as a bringer of chaos and destruction and as a weapon to save the World. However, ages later, Xehanort came upon the story of the Keyblade War and resolved to recreate the χ-blade to cause a second Keyblade War.
Truth about the War
As revealed in Kingdom Hearts χ, the war had already been going on ever since The Master of Masters was a boy, with him confirming there were other Keyblade wielders, the war itself centering between the clash of light and darkness. The Master of Masters states that the darkness was closer to a human than the monstrous Heartless it would take shape of and there were other Keyblade wielders. What happened to said wielders is unknown but they were clearly gone by the time the Master of Masters would instruct the five Foretellers and one other Keyblade wielder.
Shortly before he disappeared, the Master of Masters assigned his disciples new names and gifted five of them with a tome from the Book of Prophecies, which taught them of the event that would doom the world. However, in truth, the Master of Masters intentions was never to stop the Keyblade War as it has already been going on but instead to end it by causing the end of the world. The Secret Reports of Kingdom Hearts III indicates that had the Master of Masters not ended the War the way it did, it would have had a possibly much more disastrous outcome, perhaps leading to the complete annihilation of the worlds. He had discreetly manipulated the Foretellers with roles specifically designed to make them turn against one another and told Luxu the secret contents of the Lost Page detailing his true intentions and gave him the mission to observe these events to ensure that they will occur as prophesied. Due to the Lost Page, he watches over and manipulated the events and Foretellers, just to ensure that the prophecy of the war will come true, which succeeded in causing conflicts in between the Foretellers, who have mixed reactions and thoughts of preventing the world's end. Ultimately the Keyblade War truly began when Luxu and Ava clashed, ringing the bell of the Daybreak Town.
Fortunately, the Master of Masters had no intentions to truly end the world either, only to end the world with the final battle of the War and then have special Keyblade wielders escape to another world and recover the scattered light so that the world may be reborn and the fighting cease if only temporarily. To this end, he assigned Ava to gather Keyblade wielders that would be called the Dandelions all so that the children will create new worlds through their hearts and ensure the survival of the wielders. The Master of Masters also handed Ava the list containing wielders that were meant to become new union leaders, with the known leaders being Ephemer, Skuld, Brain and Strelitzia, although she was somehow replaced by Ventus, and specifically instructed her to only have Strelitizia inherit and read the contents of the Book of the Prophecies and to instruct him into keeping the Book's contents a secret from all others less the world be dangered.
In a conversation with Luxu, the Master of Masters revealed that he and the Darkness were old friends, and that his plan to truly defeat the darkness would like lifetimes and the destruction of space and time, hence the Keyblade War. He reveals Darkness cast aside it's physical form in order to end the world, but it's will would fade without physical vessels. He tells Luxu the the traitor mentioned in the Lost Page served a purpose so that out of the thirteen original darknesses after the Keyblade War, he trained his six apprentices and himself to be vessels for the strongest of the thirteen but with strong enough hearts so they wouldn't be possessed, and for the new Union leaders to be the remaining vessels. The traitor, Luxu, was needed to sow seeds of darkness in the Foretellers by turning on each other. Before he disappeared he talked with one of the darknesses. He explained that the data Daybreak Town would be destroyed when the arks where used and put into sleep to trap the willful darknesses. The Master of Masters revealed that the true purpose of the Keyblade War was so that after the end of the world, he and others would travel into the future through the arks and other means. He explained to travel in the future one would lose there body in the arks and to successfully reform, there needed to be a waypoint, the Book of Prophecies, a medium at the destination, the Gazing Eye keyblade with his eye, and someone with memories of the person at the destination, Luxu, to rebuild the person. The Darkness and the Master of Masters compliment each other on their genius and each asked what the other is truly up to. The Master of Masters explains he did not let the darknesses see everything in the Book of Prophecies, and it only contained what his eye in Luxu's keyblade saw, and only the important stuff to jot down. He revealed he did see a world in the future he couldn't conceive. A world darkness and light couldn't control, a world of fiction.