As far as the initial story goes:
The main location for this campaign will take place in two planes, entitled the mortal realm and the imortal realm by their occupants. For many centuries, if not milennia, these worlds have believed that they were fairly alone in the multiverse. However much like earth has myth of long lost magic, and continents, so do they. Some scholars even know of earth and several other realms but they have been essentially lost. Specifically by lost i do mean lost, as in no one actually knows how to get there.
The mortal realm is your stereotypical dnd set up, with the rise and fall of kingdoms, adventuring heroes, and good vs. evil. Also mortals in this campaign basically encompasses humans, animals, and most creatures with a short life span. The imortal realm on the other hand does not support most of these. Immortals live for considerably longer, or in some cases do not die of old age. Their realm does not form kingdoms but rather is much more of an outlands planar set up. They have a rather large ammount of space and do not dwell on power or territory as much. Instead they form cabals, which are essentially organizations of various immortals regardless of race working for specific goals. For the most part the immortals leave the mortal realm to its own autonomy. With the exception of very few cabals, the primary one being Concord. The Concord cabal primarily concerns itself with overt threats to the mortal realm, but will also dink around with varying degrees of favoritism (much like the greek gods did).
Several years ago, they dont know exactly when, portals began springing up around the mortal realm. While portals are not new to the inhabitants of these worlds, the new portals destinations were. Specifically the portals known as Terrai, Aldretch, and the Katar portals. From these portals began issuing an army that began assaulting the mortal realm with much more power, and also is very organized. The first assault attacked the largest elven city in the mortal realm, edarth. After that the invading army begin sweeping around destroying whatever remained in their path. Also the invading army is the only mortal forces that have been known to be able to wield blood magic. None of the attempts to close the portals opened from this or the other worlds have succeeded, with unknown reasons.
The remaining kingdoms in the southwest continent have banded underneath the more powerful kingdom of Tirasnova, creating the Coalition. While the smaller kingdoms are hardly well represented, the coalition is much more of a multi nation organization (like NATO) that follows the command of the main kingdom (the US). On the northern continent kingdoms do not exist. Instead they have formed city states, with a much more anarchal feel outside the cities. These city states have been virtually overrun by the invading forces. The eastern continent is almost entirely controlled by the Aryen Nation, with only some of the rudlands bieng independant.
The three main powers in the mortal realm (concord, the coalition, and the aryen nation) have banded together to help fight against the invading forces. Most of the army fighting has been performed by the coalition who have the strongest army out of the three, concord doesnt actually have an army. The other two have primarily been focusing on research and exploration. This primarily refers to the other portals leading to other worlds that have been discovered. So far they have found a grand total of 5 worlds that are accessible by these new portals. One of these worlds is earth, one is the invading army, and the other three are other worlds with varying forms of magic and technology.
The Aryen Nation and Concord have been focusing on sending people covertly through these portals to investigate these other worlds. These efforts have been very covert, since they do not wish to have any more worlds join in on the war. Their efforts have been very centered around aquiring technology, which these worlds somewhat lack (but the invaders posses), and recruiting new magic sources to attempt to close the portals.
The forces of the coalition are concentrated into stregthening their army as much as possible. All available magic users are being used as troop support or battle mages in army regiments. Concord does not even posses an army, rather than a kingdom style of set up they are centered around a council of elders. Underneath the council they have a higherarcy that could resemble military standings, but is entirely based on magic progression and prowess. Finally the Aryen Nation is much more of a typical kingdom set up, but their magic users are not as integrated into the common people. Magic users in the Aryen Nation are usually affiliated with either The Eye or The Hand. These two organizations are the covert operations of the Aryen Nation. The Eye is an incredibly secretive organization that spies on others and themselves, much like CIA and FBI. Members of The Eye do not reveal who they are and if they are identified they usually claim allegience to The Hand. The Hand is the organization that is arrayed much like a separate military organization. While it does not have the full force or numbers of the military, they are much smaller and more specialized. These squads travel around and carry out various missions that The Eye have seen a necessity for.
Characters are allowed to be from any of the worlds mentioned so far, with the exception of the invading forces world. If you chose one of the other three come up with some backstory and set up for that world, no technology past what earth has though, and magic of whatever you wish. There are no ECL's in this system, rather than that use the advantages system to give your self racial whatevers.