The Aeth'er Wars (天地戦争 Tenchi Sensou?, "Heaven and Earth War") is the name given to the central conflict that took place around 1,000 years prior to the events of Tales of Destiny. Its impact greatly affected the planet and future generations of the races involved in the war. During Tales of Destiny 2, the latter half of the game focuses heavily on the conflict, as the protagonists journey through time in order to quell the wrongdoings of the antagonists who wish to rewrite history.
Around 1,000 years prior to the events of Tales of Destiny, a large, Lens-infused comet collided with the planet, enveloping the sky with a cloak of dust clouds. This, in turn, plunged the world into an ice age that threatened humankind. However, with the mysterious and powerful Lens of the comet, the crisis was averted. The people used the Lens to create and power a massive floating continent known as the Aethersphere, which hovered above the Er'ther Lands. The Aethersphere was home to the Aeth'er race, while the the Er'ther Lands were inhabited by the Er'ther race. As hostility grew between the Er'ther people and the elitist Aetherians, the Aeth'er Wars spurred. The Aeth'er race, led by the Aetherian ruler Kronos, possessed a large and powerful, sword-shaped superweapon known as Belcrant, which protruded from beneath their aeropolis capital, Dycroft.
Using Belcrant and their superior technology, the Aetherians struck down all who opposed them until a group of Aetherian scientists, disgusted with their people's elitist behavior, descended to the Er'ther Lands and developed sentient swords known as Swordians that ultimately led to the defeat of the Aetherians. As a result of the war, the Aethersphere and its aerial cities were destroyed and plunged into the depths of the ocean, and its populace was exiled to the desert region of Calvalese. This left the Er'thers as the only sentient race inhabiting most of the planet. The modern population of people are descendants of the Er'ther race, and the Aeth'er race has long been forgotten by the common people, though they comprise nearly the entirety of Calvalese's population.