The single most important event in the history of the world occurred roughly 50 years ago. A world war was in its final days. A century of magical conflict had scarred and blasted the landscape, producing many monstrous creatures and warping huge armies of men into abominations.
Some desperate group of wizards called down a Doom to end the war. They summoned forth Zbraxian, Lord of Change, to alter the world and end the war. They tried to bind a being of elemental chaos to reshape all of creation to their design. They failed.
Bound by the evil of these sorcerers, Zbraxian became corrupted. As the magics began to reshape the world, he lashed out with his great Hammer, shattering reality. Volcano’s across the world erupted as one. Huge tidal forces ripped across the oceans. Earthquakes rent the world asunder.
Where Zbraxian’s hammer hit the earth, a great Rift was formed. Now a massive font of Eldritch energy streams up into the boundless sky. Heat rolls off of this rift in waves, like standing too close to a forge. This energy is the raw essence of chaos, the base energy from which all the universe was forged long ago. It twists and corrupts any normal matter it touches, breaking down form and bringing chaos into the world.
It was a full year before nature settled down. The entire planet was completely reshaped. What was once a single interconnected continent had been shattered into a few moderate landmasses and countless thousands of tiny islands. The weather of the world had been utterly altered, seasons lost their power and climate became based solely on distance from the Rift.
The Old World
Before the Rift and the Apocalypse that followed, this world was very much like Forgotten Realms. It mostly consisted of one huge super-continent with various warring factions on it. There were many islands and sub-continents around, but most of the power was on the mainland. There were civilizations that rivaled those on the super-continent that had been discovered on far away lands, but contact with them was difficult due to distance. Humans were by far the dominant race, and most of the more monstrous humanoids had been pushed to fringe territories or killed outright.
The world was very much run by magic. Clerics and Wizards tended to either be the ruling class or to be the power behind the throne. Casters were very jealous of their power, and those few who had amassed enough to rule their parts of the world were very keen to keep any potential rivals under their control.
This lead, inevitably, to a century of escalating magical warfare between the various Arch-Mages and Heirophants in the world. The common people suffered under the yolks of these mages, and many armies were used as guinea pigs to create ever more powerful magical soldiers.
Records from this time are very very incomplete as most great cities and libraries were destroyed in the Apocalypse. There are many non-humans still living who remember the world that came before, of course, but they only know what their mortal memories retained.
The five decades since the Apocalypse have been an understandably tempestuous time. At first it was small isolated groups of survivors eking out a subsistence in a world grown suddenly harsh. The massive climate changes that followed the Rift caused many to die. The creatures that the upheaval unearthed caused many more to follow. Sadly, most of those that died were at the hands of their neighbors.
Eventually, powers began to reassert themselves. It was an age for heroes, and tyrants, and those who would prove to be both. Those with might began to carve out niches of civilization. Cities were rebuilt, farms were cleared, and life returned to some very small semblence of normality.
Old animosties have been left behind, for the most part. The panoply of sentient races have more or less come together so that they can survive in their world gone strange. There are still wars, and power struggles, and racism. But those are luxuries that few can afford.
Despite this the world is still a terrible, hard place. Those that have the power oppress those below them. Many peasants will do literally anything if it means keeping the wolves at bay, and their feudal lords know this. While inside of a given City, Kingdom, or Empire various people may get along, outsiders are looked at with a deep suspicion. Disease and starvation are big enough threats without foreigners taking your food, land, or resources. Slavery is rampant. A conquered group will gladly take the lash rather then risk being forced out of their homes.
Wilderness is death. It is starvation, and predation, and madness, and finally death. This is what children now learn in the crib, what adults dare not forget.