The Ancient World
This all needs reconciling with the Timeline.
The Eldar-ruled World
It is said that the Eldar were the ones that brought arcane magic into the world, and that their close proximity to the gods is what enabled the granting of divine magic as well. Eldar are said to have fought toe-to-toe with the worst of the demon lords and devil princes, and supposedly stood alongside the gods when the fiends were banished to the Outer Planes and the Compact (which prevents fiends from ever calling the mortal plane home) was imposed upon them. Great works of architecture, art, music, craft, poetry, and even dance were said to be the hallmark of Eldar culture and presence.
The population of the Eldar never rose beyond a million, even at their peak, and in order to carry out the various tasks that were required, the Eldar forged the firstborn races, dwarves and elves, to assist in their tasks: dwarves, with their affinity for the earth, and elves, with their affinity for the woods and the air. It is rumored that other races were also forged to care for the air and the seas, but if so, these have long since disappeared.
Despite the aid of the firstborn, the Eldar realized that they required a more adaptable, sturdy race to carry out a variety of tasks that had no common purpose or environment, and thus were the first humans born. Shorter-lived in order to encourage their adaptability, humans quickly became the servant race of the Eldar, and dwarves and elves were given more leeway and latitude to carry out their tasks without Eldar oversight.
Not long before the Fall, the Created emerged into the world, though their origins (aside from the dragonborn) are not thought to be Eldar-created.
The Eldar and the Hordes
For as long as the Eldar have been in Azgaarnoth, so have the Hordes. Some theorize that the Hordes are a natural part of the world, others believe they came when the Eldar began to travel through the stars and the planes. Either way, the result was the same: a brutal and incessant conflict that began five millennia before the Fall, and continued long after. Some scholars theorize that the Eldar and Hordes are symbiotes at some cosmic level, others that the Hordes are refugees from an extraplanar conflict. Regardless of their origins, the Hordes have plagued Azgaarnoth in some way since the beginning.
Originally, the Hordes were limited to eastern Yithi, but as time passed, they were able to escape the "containment"
The Fall
At some point in the distant past, the Eldar suffered a great Fall. It is not clear what the nature of this event was, however; legends speak of a disease, or of a cosmic upheaval, or even of a betrayal from within, but no concrete evidence has been found that supports any of these theories beyond wild conjecture. Regardless of its cause, the Eldar--apparently greatly weakened in number and power--withdrew from the world almost entirely, centering their presence in the world around Mt Bezulb in Shemkanar near the border of Zabalasa and Alalihat. Centuries would pass before an Eldar was seen outside of their home, and visitors were quietly discouraged from visiting.
Humanity's Ascent
Greater and greater autonomy was given to the human servant race, and for a long while, humans were able to oversee the Eldar's empire without direct intervention. Throughout the tumultuous milennia that followed, humans always sought to govern in the fashion that the Eldar had impressed upon them, and all seemed to be well aside from the Eldar's departure.
(Describe the working relationship between humans, dwarves, elves)
Humanity's Struggles
Over time, however, stresses emerged as new situations arose that required responses that humans were simply unable or unwilling to provide. The Hordes grew more powerful and restless, and the absence of the Eldar to coordinate and lead a response led to greater and greater commitment of precious time and humanity to combat them. Whispers amongst the humans (and dwarves and elves) began, questioning why the Eldar had tolerated the presence of the Hordes for so many centuries. When the Hordes descended into the Underdark, first into the Daw mountains in the Al'Uma lands, then later on Liria itself, leading to the Exodus, the questions became accusations. Humans, the visible representatives of the Eldar's governing, had no answers. Dwarves withdrew from partnership with humans, angry at the lack of an answer and solution. Elves sought to negotiate the return of the dwarves to the world, and a greater commitment of force from the humans to battle the Hordes in the Underdark, but humans were pressed to the limit and dwarves could not shake their distrust.
In time, the various races realized that an Eldar had not been seen in over five centuries, and it was a sobering realization: The humans and the firstborn were on their own, entirely.
The Exodus
The Returns
The Ancient World (up to the Fall)
The Eldar were known to create the world, and chose to settle within the boundaries of what is now known as Azgaarnoth. A land of low forests and grasslands, punctuated by a spine of mountainous activity stretching through the center, the Eldar created a beautiful--if sparsely populated--paradise for themselves. Dragons, awesome and beautiful beings of majesty and might, were seen as partners and companions, in much the same way that a mage or druid would partner with a companion, save that dragons were equally intelligent and powerful.
As the Eldar moved through the world, they found that numerous tasks involved around upkeep, maintenance, development, and growth were distracting from their larger purpose. Convening, they decided to give life to two new races of creatures "in the Eldars' image" to serve as stewards and caretakers of the world while the Eldar went about their purpose. Thus were the "Firstborn", the elves and dwarves, given life, one to concentrate their efforts on the natural world around them, the other to focus their efforts on the earth beneath. For thousands of years, elves, dwarves, and Eldar worked side by side to heighten and enhance the paradise that came to be known as Azgaarnoth.
Ancient lifespans
Ancient records and histories hold that these Firstborn lived much longer than their current kin. It is said that the original elves--what some call the "pure elves"--were in fact ageless, and lived for as long as they chose, barring any sort of physical harm broght to them. The first dwarves, too, were rumored to be ageless, although fewer tales of such "timeless ones" are told. It is theorized that their close exposure to the Eldar granted them longer lifespans--or else it was simply that the world was simply a safer place.
During this time, the Eldar and the Firstborn lived in a veritable utopia, crafting wondrous works, engaging in high magic, and possibly even journeying to distant planes and stars. It is theorized among a few scholars that it was this latter research that led to what came next.