The Timeline

Time Immemorial:
The χ-blade and Kingdom Hearts have been ever present. Kingdom Hearts is said to be the heart of all worlds, and the source of ultimate power and wisdom, as well as the source of all light.

Age of Fairy Tales:
People begin to form Keyblades in the image of the χ-blade.

One year Before the Keyblade War:
The Keyblade Hero known far and wide; "Cyrus" vanishes suddenly and without a trace, his sword "The Kingdom Key", and his castle unexplainably vanish along with him, leaving a crater where the home once stood.

The Keyblade War:
War breaks out between Keyblade Wielders. Darkness overtakes the world, the χ-blade is shattered into seven fragments of pure light, and thirteen shards of darkness. Kingdom Hearts vanishes. The Keyblade Graveyard is the grim reminder of this terrible war of greed.

The World Revival:
The World is revived by the light within children's hearts, some decide to use Keyblades to defend this light.

The Age Before Sleep:
Xehanort grows up on Destiny Islands, as a young man he is visited by his future self's Heartless, who grants him the power to traverse through time and tasked him with gathering twelve other incarnations of himself from across time.

Upon accomplishing this task, Xehanort returned to his proper place in time and relinquished his memories of the future, but retained his desire to travel to other worlds. He eventually found a way to depart his home world and arrived at the Land of Departure, where he encountered a Keyblade Master. Under this master, he began training as a Keyblade wielder, along with his fellow pupil Eraqus, who Xehanort eventually came to see as a brother.

Birth by Sleep:
The events of the game go by largely as one expects, however; Sora, Riku, and Kairi make no appearance.
Terra loses his body to Xehanort.
Ventus loses a fragment of his heart, but is aided by a now unknown being (as Sora is not involved)
Aqua is thrown into the Realms of Darkness after a fierce battle with Xehanort, who stole Terra's body.

Time Incomprehensible:
Aqua wanders the Realms of Darkness, shielded from great dangers with the help of the lingering wills of Terra and Ventus. Her legend lives on through word of mouth, some still believe that she could come back... Whether of her own accord, or through the aid of others.

Present Time:
The Start of Kingdom Hearts 1, Sora, Riku, and Kairi are nowhere to be found. Instead we are left with... You. This is where all of our stories begin.