Originating from Dungeons & Dragons 4th edition, the Dawn War is an ancient battle from the World Axis cosmology, fought at the dawn of time (hence its name). In a nutshell, after the Primordials arose from the Elemental Chaos and created the mortal world, the Feywild and the Shadowfell, the Gods descended from the Astral Sea, stabilized these new planes, and seeded them with life, creating all non-elemental or immortal beings in the cosmos. This meddling in their creation ultimately incensed the Primordials, who reacted violently to the intrusion.
The Gods of the Nentir Vale setting are also known as the Dawn War Pantheon, as a result of this over-arching piece of lore. This term is used in Dungeons & Dragons 5th Edition, where the Dawn War Pantheon was, for some reason, relegated to page 10 of the DMG rather than to Appendix B in the PHB.
For a complete accounting of all 4e setting lore and historical information, see here: https://drive.google.com/file/d/0B2mLfpEGKv-Sb29tN2tBYVBWZzA/view
The War at the Dawn of Time
It's unclear whether the conflict broke out immediately, or if it actually there was initially a tentative peace; lore scattered throughout issues of Dragon Magazine, Dungeon Magazine and various splatbooks suggest that at first the Gods and Primordials actually got on fairly well. For example, minotaurs were created by Baphomet when he was a Primordial as part of a bid to take the role of God of Nature from Melora, various elemental beings like genies, hellhounds, bullywugs, and even some animals were born of the Primordials in imitation of godly efforts - manta rays are said to have been made by Demogorgon before he turned into the Demon Prince!
Inevitably, though, the Primordials grew to resent their Godly competitors. Many sources imply that it was the creation of the first dragons by Io that provided the first major spark that ignited the conflict; imbuing his creations with powerful elemental magics, Io symbolically claimed dominion over all elements and, by extension, sovereignty over the Primordials themselves. Which they did not appreciate in the slightest so... yeah, nice going, dragon-boy!
Of course, the Primordials were far from innocent themselves; the first major blow in the Dawn War was fought over what the dwarf race now remembers as the Age of Chains, when giants and titans descended upon Moradin's creation of Stoneroot, the mightiest mountain in the world, and besieged it, seeking to enslave the dwarves and ultimately provoking retaliation from Moradin when he became aware of his creations strife.
In the end, the Dawn War was inevitable; the mortal world was too stable for beings born of endless chaos, and they sought to unmake all that was in order to start again, a continuation of the same cycle of creation, destruction and recreation that dominates the Elemental Chaos. Existant rivalries merely added fuel to the flame, and when the Primordials sought to unmake the World, the Gods declared war. It was a bitter conflict that spanned all of creation, seeding great destruction; the Lattice of Heaven was torn asunder and the Rune of Stone Eternal was stolen by Primordial agents, forever after scattering the Gods across the Astral Sea and breaking the planned mechanics for exalting their devoted worshippers. Abominations, unholy living weapons, were birthed on both sides of the war in order to find some super-weapon that could shatter the ranks of their enemies - ironically, Carceri, the Astral Dominion where the Gods bred their abominations, would ultimately be repurposed as a prison to hold them forever. Death's Reach, at the core of the Shadowfell, was sealed shut by Primordials, in hopes of trapping the souls of the dead to consume them for power. Whole worlds perished in the conflict; the Astral Dominion known as the Forgotten Sanctuary is the only remaining continent of one of these dead worlds, whilst Athas was doomed to its ultimate fate by becoming a world from which the Primordials successfully drove away the Gods, opening it up to the taint of defiling magic.
Initially, the war did not go well for the Gods; only when the god Achra managed to convince a small group of gods to unite under his leadership and slew Tabrach-Ti, the Queen of Bronze, did the Gods find a unifying leader who could help them fight more efficiently. Whilst some remained aloof, it was to their cost - Gorellik was killed and his gnolls stolen by Yeenoghu, whilst Io, who fought alone throughout the Dawn War, ultimately perished at the hands of Erek-Hus, the King of Terror. So integral to victory did Achra's leadership become that he became known by a new name, a title bestowed upon him by the fearful Primordials: Bane.
The Dawn War only grew more complex and straining on the Gods when a third party grew involved; the demonic creations of Tharizdun united around Demogorgon and hurled themselves into the fray. Although indiscriminate in their hatred, they had a particular enmity for the denizens of the Astral Sea, and the betrayal of He Who Was by Asmodeus did not help matters much - unless perhaps it did. Neither did the Kinstrife Wars, in which Corellon and Sehanine fought with Lolth after she betrayed them, causing the eladrin race to splinter and creating elf and drow from different factions.
So great was the conflict that the Primal Spirits, entities born of the mortal world and perhaps an unwitting creation of the Gods, ultimately rose up to add their own might to the fray, determined to protect that which had given them life. Though a comparatively minor element, their help, alongside other factors such as the rebellion of the genasi slave-soldiers and "The Desolation", a genocidal cleansing of the elementals whom the Primordials reforged into Archons, was one of many tipping points that ultimately brought about divine victory.
The tide turned when an exarch of Moradin, in alliance with seven Bahamutian archangels known as the Wind Dukes of Aaqa and a benevolent fiery Primordial named Bristia Pel, crafted the Rod of Law and used it to banish Miska the Wolf-Spider, the Prince of Demons. This shattered the unity of the demonic hordes, causing them to fall into scattered mobs and constant infighting. With this threat ended, the Gods could focus entirely on the Primordials, who subsequently found themselves riven by dissent and betrayal. Primordials who had always been on the side of the Gods, such as Chan, made their influence more openly felt, whilst other Primordials betrayed their kin in pursuit of power or survival, as was the case with Ubtao the Deceiver. The nagpas, created as powerful sorcerous minions, betrayed their creators en-masse, for which they were cursed into their present hideous shape.
With the death of the Primordial Sehil at the hands of the god Kord, the final battle of the Dawn War was ended in the Gods' favor.
Of course... fate has a tendency to work in cycles. All too soon, with the Primordials defeated, the Gods would turn on each other, fighting what would be called the Godswar.
Participants of the Dawn War
The list of powerful beings who partook in the Dawn War is a long one, and includes pretty much all of the major names in 4th edition's cosmology. This segment should help to keep them in straight, including their ultimate fates.
- The Raven Queen
- He Who Was
- The God of Humanity
- The God of the Word