When the god Aion created the world of Atreia, he created the draken—powerful dragon-like beasts tasked with safeguarding the humans; performing Aion’s will on the planet; and protecting the Tower of Eternity, Aion’s physical presence on Atreia. For a time, the draken obeyed Aion; but over time, they began to enjoy their power, ignoring their duties and abusing the humans. Aion took notice, creating the twelve Empyrean Lords in response. Angelic in appearance, the Empyrean Lords were demigods who walked amongst humans, and used a force called “Aether” to create a powerful barrier around the Tower of Eternity, protecting all of those within. While the outside world continued to be ravaged by the draken, who had become the more ferocious Balaur; the humans within the barrier managed to tap into the Aether, gaining their own powers. In time, they would become known as the Daeva.
As time went on, the Lords decided that they had to be more aggressive in stopping the Balaur. With the number of Daeva growing in size, the Lords decided to form an army, with ten of the Empyrean Lords leading the Daeva into battle; while the remaining two, Siel and Israphel, protected the Tower of Eternity (thus earning the title “Tower Lords”). This conflict between the Balaur and the Empyrean Lords would come to be known as the Millennium War, which led to no real progress by any side. As the war progressed, a faction of Lords began to view the war as unwinnable, and Lord Israphel proposed a discussion of peace with the Balaur. This surprise proposal drew criticism from within the faction; after a lengthy and heated debate, seven of the twelve Lords became the winning majority to move forward with the plan.
However, for reasons unclear, the negotiation failed. When the Balaur arrived at the Tower of Eternity, a commotion broke out, killing a Balaurian captain; they remaining Balaur, enraged, marched upon and destroyed the Tower, which set off a chain reaction that threatened to destroy the planet. However, Israphel and Siel made the ultimate sacrifice and gave their own lives to protect Atreia. The world was shattered into two “hemi-shells”, with a dark Abyss laying between it; but was held together by the aetheric field created from the Tower Lords’ sacrifice.
While the Balaur were banished to the Abyss, the Empyrean Lords found themselves in conflict with each other. Two groups were formed, each with five Lords; the Seraphim, who had proposed the peace solution and blamed the others for sabotaging the peace negotiations by failing to agree to them; and the Shedim, who blamed the Seraphim, believing that their weakness and their proposing of the peace talk allowed the Balaur to gain the upper hand. From that day on, the two sides became bitter enemies.
The Shedim were exiled to Asmodae, the dark and harsh top half of the planet; while the Seraphim Lords settled in Elysea, the light and beautiful bottom half. They both took their humans and Daeva with them, and over time, they adapted to their new world and declared the opposing side to become their mortal enemies. Those in Asmodae became the Asmodians, gaining dark features and hostility towards outsiders (though they are generous and supportive to their own kind). Those in Elysea became the Elyos, growing even more beautiful and believing themselves to be Aion’s chosen people (although they have grown arrogant). From that day on, they would wage war for centuries as bloody enemies.
Taken from Wikipedia.