The year is 2452. The world is large, a merger of two planets, our own, and another planet, known as Gemina.
Earth. Earth stands as a cradle of life, young, vibrant and fertile. Placed perfectly in orbit around the sun, the earth supports a massive ecosystem. It is a home to the human race; They reign as the definitive masters of their world. They build great structures and form strong bonds. As a united people, they lived on the edge of a golden age. The events of Earth played out almost exactly as you have read in your history textbooks, with the following exception: a curious discovery in the early seventies, shortly after the celebration of the American moon landing. A curious planet known as Gemina was growing ever more likely to collide with the earth, and paranoia and fear began to spread among humanity as to what that meant for them... and their lives.
Gemina. Similar in many ways to earth, but also opposite to it. Millenia ago, beings which could only be compared to the "dragons" of earthen folklore ruled the lands. Gifted with a "soul", an organ of pure energy, capable of manipulating the very rules of reality, these dragons had a keen mastery of technology of all kinds. They obliterated the concept of disease from their lands, they created entire races, inspired from the humans and mammals seen on earth, whose only purposes were to serve and worship them.
However, tensions arose between the dragons, their powers granted them prosperity, but it also granted them resentment, envy, and distrust. They could no longer form relationships with each other, like their slaves could. The age of dragons ended when these tensions reached a boiling point, and "The Weapon that has no name" was fired, condemning the dragons to near-extinction. Their slaves, now emancipated, rebuilt the land. They did not have the same curiosity of earth that their progenitors had, they viewed it as simply another planet that happened to have life, until they realized they were going to crash into it.
In 2022, the planets collided, but instead of the armageddon that was promised, a miricle happened. Instead of the cataclysmic destruction that two planets crashing into each other would expect, they began to merge into one. While the death toll was still astronomical, it now set up hope that both planets could rebuild once more as a single planet. This event became known as "The Joining".
Initially, tensions were rocky between the two sentient factions. They resented what the others had. The Geminans inherited their souls from their dragon progenitors, but in a world without disease, their immune systems atrophied and withered into nothingness. Meanwhile humans could never have evolved souls in the way that the Geminans were granted them when they were first designed. These tensions would smooth over as an event dubbed "The Great Exchange" in 2050, granted humans the souls of Geminans, and granted Geminans the seeds of immunity to disease.
Over the next four centruries, the world rebuilt, new empires were formed. Old empires were rediscovered and revived. The world has begun to truly know peace.
However, there are still issues that need to be attended to. There are still mysteries from the pre-joining world that still linger, waiting to be solved by adventurers. There are tensions between the nations, potentially dooming them to repeat the mistakes of the past. Yet, there is still hope that things will turn out well. There has to be.