You know the fantasy cliché where the heroes avert the destruction of their civilization? This is not one of those worlds. Think of the final third of The Silmarillion, or Act V of Diablo 2.
The world of Aldebaran was once a world largely at peace. After millennia of conflict, the evil gods were defeated and had retreated into obscurity. It was not a world without war, as the different kingdoms vied for petty gains or they fought the occasional uprising of goblin-kin. Twenty years ago, an unknown evil force opened a portal to another world. Through this portal came a huge army of orcs, tieflings and other evil beings. This army swept through the human lands destroying everything in their wake. Many human survivors fled to the mountains where dwarvish forces were able to hold off the invaders. An alliance of all of the goodly races was formed with the purpose of destroying the orcs and their gateway. They were joined by another race from the other side of the gateway, known as the dragonborn. A ferocious battle raged at the Gate and all appeared lost until a small group of adventurers, assisted by the dragonborn, destroyed the gate, which cut off both the orcs and the remaining dragonborn from their home world. The goodly forces were still outnumbered and they were forced to retreat to the mountains once again. Almost all of the human lands have been overrun and are permanently in the hands of the orcish invaders.
Every spring when the snow blocked passes open, the dwarves prepare for the spring offensive by the orcish forces. And every year the dwarves take losses they cannot replace and the goodly peoples come closer to that day where valor will go beyond recall. With evil dominating the world, ancient and forgotten creatures have reawakened from eons of slumber. Creatures of pure nightmare roam the lands pursuing their own grisly agendas. Evil gods gain followers and power daily. Giants have grown in number, and the dragons, creatures of magic, have begun to take sides. No one knows what drives the orcs on such bloody campaigns each year, or why they invaded in the first place. It is suspected that they are taking orders from a higher power.
Stout and hardy adventurers are needed to defeat the forces of evil. Many of the most famous heroes are members of the armies of the different races, where they gained experience and fame fighting the forces of darkness. Even though the main threat comes from the orcish invaders, the reawakened evil native to Aldebaran also cause much suffering. Giants, dragons and drow have all returned
Magic is fundamental to this world. There are nexuses of magic at places throughout the world where great reserves of power can be taped into. It is said that these nexuses connect Aldebaran to the other worlds in the material plan and also to the different planes. Harnessing the power of these nexuses may be the key to destroying the evil forces.
As per the Manual of the Planes.
Pantheon: Use the Player’s Handbook as a guide.
The powers of the gods are very active in this world and many heroes have been blessed with divine favor. With more suffering and evil in the world, many question the inability of the good deities to counter the forces of evil. New cults and cabals spring up continuously. They perform barbaric rituals; some believe that only through human sacrifice can the gods be appeased and peace restored to the world. In short, this is a time of religious upheaval where some look to the gods for salvation and others for blame.
All human civilization has been destroyed. Most of the survivors of the conquest took refuge in the mountains and have been assisted by the dwarves.
The only humans that remain unconquered are the barbarians of the hill-lands and the horse people of the plains. They are considered barbaric and barely better than the orcs, depending upon who you ask. Many barbarians fight with the dwarvish forces for glory and wealth.
There is also talk of humans that escaped the conquered lands aboard ships and who survive among the isles to the south-east. But no contact has been made with these people.
At the end of the Gateway War, the elves retreated to the safety of their forest homeland. But while the army was away, the drow reemerged from their underground sanctuaries and had sacked much of the kingdom.
The elves are a hunted people; forever pursued by their dark-elf kin through the twilight forests of their homeland.
The dwarven mountain-citadels are the only remaining organized resistance to the evil powers. The orcs have had a difficult time in their attempt to destroy the dwarves because of the difficulty of the mountainous terrain and the martial abilities of the dwarven people. The dwarves have always enjoyed their privacy, and some of their cities remain secret to this day. The alliance with the humans is often strained by the cultural differences between the races.
The dragonborn are not native to Aldebarron. They are native to the world that the orcs came from. The dragonborn call their home Draconis, and they also insist that the orcs were invaders to their world. They sent an army through the portal in order to counter the orcish armies. They were unsuccessful, and in an act of selfless desperation, they destroyed the gateway trapping the remainder of their army on this side of the portal, but also preventing orcish reinforcements. Much of the dragonborn army survived the battle at the gate and have worked with the dwarves to defend the mountains.
Trapped from their families; the dragonborn have attempted to settle within the mountains. Many have left behind loved ones who they wish to be reunited with. This makes them impatient for a victory.
During the war, the eladrin did not assist the goodly races. Their only concern was preventing the evil forces from gaining a foothold in the feywild. Many resent their continued neutrality.
Before the war, halfling villages littered the human lands. Many retreated to the mountains. Some took refuge in hidden cities. It is rumored that some work as scouts for the orcs in return for their survival.
The tiefling are the minions of the evil powers. They lead the orcish forces and act as warlords throughout the conquered lands.