The Dawn War

The Dawn War lasted a long time, ending shortly after the end of your Age of Legends. But, he started back further than that.
In the beginning, there was an egg, from it hatched Io who gave life to the world. Io created the Primordials and the gods. It wasn't long before he gave birth to the oldest race: dragons. As Io represented all views of the world, so too did the dragons.
So too did the gods. Two of these gods, Gruumsh and Corellon Larethian, were at odds with each other from the start. Gruumsh hated Corellon because of the mercurial form Corellon was blessed with. Corellon was carefree, and ignored the other gods when warned of Gruums's anger issues.
The creation of the gods didn't bother the Primordials, but the creation of dragons did. Still, they did not move to act until later.
The Chained God, one of Io's darker children, found an artifact floating through the Planes and took it. The artifact twisted and warped his mind, supposedly telling him to plunge it into the Astral Sea. He decided to create the Abyss instead.
The gods and Primordials worked together to bind him, they didn't do too good a job of it. Eventually, the King that Crawls made a prison that was capable of holding him. So, the Chained God's second in command took over for him. A Primordial named Mishka the Wolf Spider decided to exact revenge for her master's imprisonment.
Initially the Primordials had the upper hand, killing many of the gods. Then, one god had an idea: that they work together. He was Achra, and a few of the gods took his advice. The first Primordial to die during the Dawn War was named Tabrach-Ti. Her followers began calling Achra by a name that he uses still to this day: Bane.
The second Primordial died in spectacular fashion. He got thrown, literally, through several Planes before he came to rest at the bottom of what we call the Shattered Sea. He wasn't sure of the name of this Primordial, or even if he died or not, but Io had to put him in his place.
Unfortunately, that was Io's only kill in the Dawn War. Very next fight he was cleaved in half by Erek-Hus. Fortunately for the gods, his death resulted in the birth of two new gods. Tiamat and Bahamut slew their father's killer together before turning on each other. Tiamat eventually fled, and they had an uneasy truce for the War. In honor of their father, Tiamat wanted to create a race of people from Io's blood. Bahamut insisted that he help her, and the two created the dragonborn.
While the gods were fighting the Primordials, some were fighting each other too. Larethian and ol' One Eye got in a fight and the Blood-Drinker drew Corellon's blood at the cost of his eye. Why I called him One Eye. He hates that.
Corellon's blood took life of its own, and like Corellon they too had malleable forms. They called themselves Eladrin. We'll come back to them. One Eye also got some children out of the exchange too. Orcs, crafted in his image, with his bloodlust, and his hatred for Corellon.
Remember Mishka? She made a deal with this cunt named the Queen of Chaos, for more power in exchange for help killing the gods. She got shut down when seven of the Platinum Dragon's angels sacrificed themselves on the Maker's forge to craft a weapon that killed Mishka. The weapon got destroyed though.
And that's how Demogorgon became the ruler of the Abyss.
One of the Lifebringer's godly daughters, a deity formally named Araushnee, saw the dragonborn, gnomes, orcs, and humans making things of the lot they had been given in life. She, for that was what she declared herself, convinced the eladrin to take one form, so that they could acheive greatness.
They began to view Corellon as their father in truth and Araushnee as their mother. Like most children, they began to favor one 'parent' over another. The Silver Prince assaulted Araushnee, who was defended by those that favored her. They argued with their maker, saying that no entity that came from Him should be attacked regardless of how rebellious they were.
The two deities began a heated debate, each one drawing their supporters to them. Corellon became distracted, as he does apparently, and Araushnee struck at him. Some of his supporters took the blow in his stead. They became the Seldarine, and one went on to be known by others as Sehanine Moonbow.
Araushnee was cast from the Verdant Lord's sight, all the way to the Abyss. here she took a new name: Lolth. Despite being saved by the Seldarine, Corellon felt betrayed, and cast out the eladrin; sending them to live a mortal life here on the Material Plane. Those weaker eladrin that favored the Spider Queen took to the Underdark, afraid of being hunted by their peers.
They weren't. The banished eladrin wailed at their misfortune, eventually going their seperate ways; each trying to find a way to please their father. Some moved to the Feywild, and continued to call themselves eladrin. Most stayed on the Material Plane, and began calling themselves elves.
Things were quiet for a while after that, the Seelie Queen and the Mother of the Wilds created a new race of sentient beings. Unfortunately, the lull in the War was over, so they were abandoned. You call them halflings now, and they only survived because Lady Luck decided to scoop them up. Apparently she has a soft spot for underdogs.
Dwarves were made next, as bait for another Primordial. He was beheaded by Bane and left to wander the Astral Sea.
Then the Nomad's Rite started being created. The Stormfather was hunting this Primordial named Mual-Tar. Couldn't find him. He got mad, and started smiting the mountains that were once there, leaving the few surviving giant kin to become nomads. Mual-Tar eventually was lured out by Pelor and the Dragon King and imprisioned by the Maker.
Then the Nysian Rebellion happened. The Raven Queen ascended to godhood by taking the power of the fallen goddess of fate. She then killed the then god of death, Nerull. This had never been done before, a mortal ascending to godhood that is, so some of the gods decided to shower her with gifts. Kord stayed out of it. The biggest fool of them was Corellon, who decided that one of the banished wouldn't overstep herself with him, and offered to grant her any request. Already quite insane from Nerull's 'tender' affections, she asked to be the gatekeeper of the dead, that souls going in either direction had to be filtered through her after death, before rebirth, and so that the miracle of resurrection would in fact be a miracle rather than a frivolity. That's why only the Raven Queen can do resurrections. Before that, any priest with enough magic energy could do it. It was around this time that the shadar-kai started to appear.
Then that long ass winter came. Kord, who at the time was allied with One Eye, the Dragon Queen, Zehir, and a now dead goddess named Khala got in a fight with Moradin. They made the Spine, and the Stormfather accidently did another genocide. Destraught by what he did, Kord turned cloak so to speak and joined his brother Bane, Pelor, Moradin, and Asmodeus and crushed his former allies. The Raven Queen decided to take Khala's power too, making her the goddess of winter.
The next battle of this conflict was the last battle of the Dawn War. Kord slew the Primordial Sehill with his barehands, shattering the Nomad's Rite into what it is today, genociding many tribes. The remaining Primordials were imprisioned, and their counterstroke changed the world. Then, the Emperor was slain and the Trust was enacted, bound to the blood of Nicolette Firious, and the gods were made unable to manifest their presence on the Material Plane or interfere directly in the goings on of the mortal world. Some of them still send avatars, physical manifestations of a fraction of a gods power.
The only god that the Primordials didn't bind in this way was the King That Crawls. Only he has the keys to the Chained God's prison, and they feared he would loose him on the Planes again. Thankfully, he decided to make his home in the Lower Dark, so his presence doesn't effect the world too much.