The Great War is a war that took place ten years prior to the events of Tales of Vesperia. The war was fought between the Entelexeia, a wise, long-lived race that keeps the amount of aer in the world of Terca Lumireis in balance, and the humans.
The humans of Terca Lumireis use a technology known as blastia, which is fueled by aer and was created by the ancient Geraios Civilization, a civilization of Krityans who can communicate with the Entelexeia. The humans greatly favored the convenience of the blastia. One day, a Krityan man known as Hermes invented the Hermes blastia, which was more powerful than the traditional blastia and absorbs several times as much aer. The combined aer consumption of the ever-popular traditional blastia, and the testing of the Hermes blastia brought the aer levels to a catastrophically low amount. If the level of aer could not be restored back to normal, it could awaken an apocalypse the Geraios named the Adephagos. Seeing that the Adephagos was awakening, the Geraios built the Enduring Shrine of Zaude. This shrine was a large barrier blastia capable of shielding the entire world from the Adephagos. After building it, Krones, an Entelexeia, lifted up the city to house what is now Myorzo. As for the Entelexeia, they decided to destroy the source of the mass aer consumption, the blastia, along with the humans, as to prevent the creation of more blastia. In contrast to the Krityans, who gave up their blastia after ascending to the sky, the humans, treasuring their blastia, fought to keep their blastia. This disagreement initiated the Great War.
The Great War took place across the world. The most notable area of fighting took place at Mt. Temza, which was the world's largest mountain and site of a Krityan city, Temza, as well as the home of Hermes and his sole daughter, Judith. With the area being a war zone, Mt. Temza, as well as the Temza, were reduced to a gaping crater in the mountain range. Two notable humans who died there in the war were Damuron Atomais, a member of the Imperial Knights and supporter of Commandant Alexei Dinoia, and Casey, a good friend of Damuron's. Seeing that Damuron could be of some use, Alexei replaced his heart with a Hermes blastia and renamed the reborn Damuron "Schwann Oltorain", who would later take on another alias, "Raven". Many Entelexeia died in the war, most notably Elucifer, who fought alongside the humans. His close friend, Duke Pantarei, was a human, and he and Duke won the war. Unfortunately, the humans feared Elucifer's power and killed him, sparking Duke's hatred for his own race.
The Entelexeia, having lost the war, were nearly driven to extinction. The only known Entelexeia still alive during the events of the story are Ba'ul, Phaeroh, Belius, Gusios, Khroma, Astal, Krones, and Spiral Draco, king of the Entelexeia. Since the war, there exists an underlying hatred between the Entelexeia and the humans, as well as the Entelexeia's hatred toward blastia. This hatred of blastia is exacerbated by the fact that blastia are made from apatheia, the crystal-like masses of aer formed when an Entelexeia dies.