he planet of Pal Tahrenor exists as a parallel Earth which followed the time-line of our own planet until the introduction of magic changed things dramatically. The people are aware of other worlds and other planes of existence, and so have appropriately named their planet "Pal Tahrenor" or "Our Planet." Pal Tahrenor has been badly scarred and the people living on it have had their reality diverge quite a bit from our own. Some landmasses have changed, cratered and fractured during an ancient war known as the Changers' War.
It was a time of much chaos, and records of what exactly happened are so scattered and varied in their accounts that nobody can agree much on what really transpired. What had caused the barrier to break down, and who the key players were is a mystery. Many of the humans must have thought they were going mad, or were actually driven mad by the exposure to the astral plane's twisted nature. Some learned to control it and became extremely powerful. Other races were introduced somehow, including orcs, elves, trolls, shape-shifters and countless other creatures dredged from the imagination of the astral plane.
There was a great war between the empires and like a bubble bursting the chaos ceased as suddenly as it had started. The planet was left scarred and twisted, cratered and pushed off its axis by explosions, but the barrier between the planes was restored. Mostly...
The magical races remained, many with the ability to move between the planes as if the barrier had never returned. Races like elves and many humans retained some sort of connection to the astral plane, able to manipulate the barrier. Their abilities were and are still limited in comparison to the powers that existed during the great war.
After the great war was over and things began to stabilize, empires reformed, many of which remained primarily human.