Great Disaster

In the Paradox Trilogy universe, thirty years before the game's events, a catastrophe known as the Great Disaster drastically altered the entire world within a day. Remina vanished off the face of the earth and was replaced by a hole known as Tartarus. The Sentora continent split apart into several pieces, destroying the Navel of the World and Heaven along with it. It created a new continent called Snow Heaven which, as implied by its name, is entirely covered in snow. Additionally, seven huge holes called Tartarus appeared all over the world; each Tartarus containing massive dungeons within, filled with entirely new and bizarre monsters called Apoptosis, and lots of highly advanced relics and technologies called Makina were discovered.

The Result
Goddess Ilias vanished and hasn't been seen since, causing the downfall of her religion and an increase in human and monster association. Finally, an enormous amount of mana filled the whole world`s atmosphere, making humans capable of using magic, thus birthing the Magical Revolution or the Renaissance era as it was called, among civilized countries.

Grangold became an extraordinarily powerful kingdom, unmatched by any other in Sentora, thanks to their army of artificial monsters and super-human soldiers. Grangold became a significant threat to Sabasa, Grand Noah, and San Ilia, by declaring war on them without reason. Rumors started to spread from soldiers returning from the war about the monstrous 'Magic King' Grangold 11th, claiming he possesses inhuman power.

After the disappearance of the Sabasa King - due to him falling into the Tartarus because of a strong gust of wind - his daughter, Sara, inherited the throne. However, shortly after ruling, Sara had a strange change of character. She has become an unhinged individual, who prioritized sex over actually governing the country, and has no interest in politics, causing vast poverty among the Sabasa Kingdom. The people have no idea what's gotten into her, but soon enough, eventual civil war erupted.

In San Ilia, a great deal of religious conflict occurred because of the King's use of Makina technology. The political force was divided into two factions. The King and his followers, who accepted the use of Makina; and their opposition, the anti-Makina faction, who kept their belief in Ilias and her prohibition against using such things. The anti-makina faction currently resides in Luddite Village, while the King's supporters continue to live in San Ilia.

Marcellus set out along with Lazarus, Merlin, and Karen to help those in need, in the wake of the Great Disaster.

The real cause
The actual reason of the cataclysm is revealed to everyone as the party progresses in Ilias Temple Ruins.

As Ilias died in the original world, her death reverbated throughout the dimensions and made her unable to carry through the Slaughter of Remina. At that time, a group of scientists were engaged in experiments involving holy and dark power. After achieving ground-breaking results, they decided to put their newly gained knowledge to use. In a new experiment, they intended to use Heinrich's sword to bring his spirit back, hoping to commune with the legendary warrior. Unfortunately, because her blood was stained on the sword's blade, they instead brought back Black Alice from the original world after the latter was defeated by Luka. Since she had both the powers of light and darkness integrated at the cellular level within herself thanks to the White Rabbit drug and her attempt to devour Ilias, she transformed into the Goddess of Chaos. Black Alice proceeded to brutally murder all the scientists present, destroyed Remina and shattered the world, and devastated Heaven itself, making it fall down to earth. This in turn attracted the attention of residents from the other dimensions, setting the stage for the events of the game.

Trivia

 * The experiments done by the scientists at Remina are a clear reference to the Large Hadron Collider, where scientists are engaged in research involving matter. Some people fear that these experiments can lead to disasters in space-time, such as a black hole opening.