The Codex of St. Asmius
As a homebrew campaign with a very specific vision, there are some fairly significant changes to the game. First, and perhaps most notably, there are no half-breed races. Each race is a separate species, and while the various races do sometimes have romantic encounters, they never result in offspring.
Second, while any race can be any class, there are some classes that are more common among certain races. Also, there may be repercussions for certain races to take certain classes. For instance, it is strictly illegal for a non-elf to be a Wizard in Immarius. (And the Elves make no distinction between sorcerers and wizards.)
Third, there is only one Church. The church exists from the earliest days of civilization; in fact, it claims to have brought the first wandering elves together to found the city of Orandorei, the first city of Immarius. During and after the war, the Church was nominally neutral, but in reality aided both sides. Consequently, the church is now politically the most powerful organization in the world. While there is only a single Church, there are several orders within the church that serve various functions. Each order is headed by a saint who founded the order, and serves a specific purpose in the church. For instance, all Paladins belong to the Order of Saint Stephen, the military arm of the church.