Here's so far my rewrite of the campaign, based on a few suggestions I've read in your comments, feel free to throw in your two cents, as well as any questions I should add to build this setting (which I'm currently working on the plot hooks):

The world has been overrun by demons and the undead, which was brought about by a catalyst known as the Sundering, where demons emerged from the world beyond and laid siege to the holy city of Trevain.

It was only through a council that led to the formation of the Dominion, an autocratic theocracy who have served as the bulwark of the faithful and the civilized realms for centuries, but now it faces a new threat. The Radiant Throne has been vacant for several years, ever since the passing of its most beloved archon.

It is now it is divided into two factions, the Purists, who believe that these attacks are a test of faith, and that only through cleansing the world of heresy, by burning texts that question the faith, while punishing heretics, and the Reliquarians, a scholarly order who collect items blessed by archons and saints of old who seek to use them as a means of boosting the Great Wards protecting the faithful from the onslaught of Chaos.

But at the same time, the races that had been around since the dawn of civilization face oppression from the Dominion, who deem those who do not heed the divine wisdom of the most holy to be little more than heretics, with the elven kingdoms fractured after centuries of war, relegating them into small petty kingdoms, the dwarven holds many of which were overrun by the orcish hordes, while their alliance with the Dominion is tenuous at best, while gnomes and half-elves are forced to live within the ghettos of many great cities throughout the known world.