There were four races of Beings:
Angels, a dauntless, militant race of winged Beings who could walk upon clouds and take to the skies in flight;
Humans, a hardy, stubborn race of Beings gifted with great strength and a deep bond with nature;
Elves, a scholarly, mystical race of Beings who could practice Sorcery through the manipulation of their Chi;
And Gods, the immortal personifications of primal forces who ruled over the mortal Beings as paragons of wisdom, strength, beauty, and power.
The oldest and most powerful of the Gods was Discord, the God of Chaos. The age of his rule over the world was one of tyranny, mayhem, and despair.
However, one Goddess saw the suffering of the mortals and took pity on them: Celestia, the Goddess of the Sun. She united the other Gods and led them into battle against Discord, the cruel Lord of the Gods. Their battle was great, hard, and devastating, and though Discord vastly outmatched the other Gods they were able to narrowly escape the jaws of defeat and claim victory against him. The Gods prepared for him Tartarus, the great prison of Hells, and sealed him in stone in its deepest Hell.
Following Discord’s downfall, the Gods waged another great war amongst themselves for his now-empty throne. Celestia emerged victorious, and sealed five more dark Gods in five more Hells of Tartarus: in the second Hell she sealed Tirek, the God of War; in the third Hell she sealed Chrysalis, the Goddess of Lust; in the fourth Hell she sealed Sombra, the God of Darkness; in the fifth Hell she sealed Sonata, the Goddess of Music; and in the sixth Hell she sealed Scorpan, the God of Storms.
Celestia then divided the world’s lands amongst the remaining Gods, ruling over them as High Princess. What followed was a more civilized and peaceful age, though the mortal races were still divided in resentment and hatred.
Celestia ruled in the city of Olympus over the land of Equestria along with her younger sister Luna, the Goddess of the Moon. However, Luna began to grow envious of her sister, for their subjects adored and honored Celestia as they did the day while they feared and shunned Luna as they did the night. Though Celestia cautioned her sister against denying the mortals their freedom, Luna demanded their adoration and honor on pain of divine retribution. When Celestia stood against her, Luna renamed herself High Princess Nightmare Moon and declared war against her sister for the throne.
The Gods all took sides between the sisters, and so there was a third great and catastrophic war of the Gods. Celestia rallied the mortal races to unite against Nightmare Moon, and together they were able to defeat her. Though it caused her unspeakable sorrow, Celestia sealed her sister in the seventh Hell of Tartarus.
The Gods all returned to ruling over their lands, and the mortals all celebrated Nightmare Moon’s defeat. Thus began an age of unification, when all of the mortal races coexisted in harmony. From that day forward, the festival of the Summer Sun Celebration was celebrated on the first day of each summer to commemorate Celestia’s victory against Nightmare Moon and the beginning of the friendship between the mortal races.