The Veil War was as short as it was brutal.
In the Age of Magic, supernatural creatures such as fey, jinn, dragons, vampires, werewolves, and human mages ruled human society, either overtly, or behind the scenes, controlling the paths of entire civilizations over the centuries. During this period, the formerly disparate factions of the horrors--considered one of the weakest of the supernatural races, ware united under the rule of the Bogeyman. The horrors attempted to carve out their place of power in the hierarchy of the world, but they repeatedly failed and were treated as little more than a joke.
Yet, during their attempts to control mankind, the leadership of horrorkind noted they were often stymied by demonic or outsider corruption. These forces represented an existential threat to creation, and it got the elder horrors thinking--not of just how to save the Earth, but also how to turn the Earth's decay to their advantage.
And so the Bogeyman approached the archangels of the Empyrean with a proposal: separate the world in a mundane world and a magical world. This would preserve the ideal of free will, which the angels loved so much, while limiting the corrupting reach of the occult. The archangels agreed, and the angels and horrors began trying to determine how best to pull off this sundering.
It was determined that the ley lines surrounding the former location of the Tower of Babel still held traces of incredible obfuscation magics, and with a bit of work, that magic could be spread across the globe. And so, the angels and horrors approached the Abbasid Caliph, who controlled Mesopotamia, and explained their plan to him. The Caliph agreed, on the condition that some humans be allowed to pierce the Veil and become members of the true world.
Unfortunately, there were spies for several other factions in Baghdad, as it was the capital of one of the world's most powerful nations, and so news of their plan leaked up
Thus begins the "Veil War". Anti-Veil forces, such as the Winter and Autumn Courts of Faerie, the Orders of Atlantis, the Seekers of Thoth, several covens of vampires, a few tribes of weretigers, numerous marid sheiks, a dozen dragons, and at least one demon prince assembled in Damascus, and formed an alliance that would break the angels plan, destroy the Abbasid Caliphate and the Kingdom Over Shadows, and send a message to anyone else trying to threaten the status quo. In response, with the angels' permission, the horrors go to seek unlikely allies, and offer the bound ifrit of Chaos freedom if they would side with the angels and the horrors. Most ifrit agree, and the seals are broken--and those who refused remain bound within the City of Brass. At the same time, the horrors also won the monetary support of the gnomes, as well as the neutrality of the Sidhe of Summer and the dwarves of Nidavellir.
The battle of the Hamad was short but decisive. The horrors, ifrit and Abbasids drew the opposing forces into attacking them, before the angelic host descended from the Empyrean, and smote the supernaturals leading the enemy forces. A majority of the opposing supernaturals were slaughtered within the first few minutes of the battle, leading most of the humans who made up the bulk of the Alliance of Damascus' forces, to surrender and plead for mercy.
The Battle of the Hamad ended with the Alliance of Damascus stunned, broken, and suing for peace.
Thus, the Veil Treaty was signed in Baghdad. Part peace treaty and part ritual, its signing ended the age of magic, and separated Earth into the hidden magical world and the ppen mundane world we know today. Mankind came to dominate the Earth through science, as the truth of magic was dismissed as lies and superstition. The Veil Treaty came to play a significant role in the development of humanity, and eventually become something of a supernatural United Nations.
The Bogeyman vanished after the treaty was signed, and handed control over horrorkind to the elected chamber of advisors. This Parliament of Shadows would come to be one of the dominant players of the supernatural world for the following millenia, and had considerable influence on modern human culture.
The ifrit were unbound, and though some went back on their word and began working against mankind, seeking vengeance for their binding, most were happy with the new status quo that put them near the top. And so the ifrit founded the City of Jewels, a trading state that would rival that of the gnomes' Kingdom Under the Mountain.
Likewise, the power of the Winter Court of the fey was broken, and Summer came once again to Faerie, with Queen Titania and King Oberon unseating the Queen of Air and Darkness and ushering in a new era for the Verdant Realm.
And, most importantly, the demonic legions were broken, and their leadership retreated to the Abyss. Since the rise of the Veil, demons have been far more insidious with the plans. No longer do their soldiers trod upon the Earth. Instead, they send succubi and other infiltrators to try and twist the souls of man toward damnation. The influence of many Outsider cults were broken as well in the years following the rise of the Veil, and while they remain a threat, until the 20th century their incursions remained few and far between.
The consequences of the Veil War continue to echo through history, and the world we live in is shaped more by this conflict and its aftermath than perhaps any other in history.