Once thing I wanted to do with The Land Between is I wanted to tie each race’s story into the war between the Eladrin and the Shadar-kai. It starts with those two races who have been fighting for dominance using The Land Between as a staging ground.
The Warforged were easy to place in the world. They were created by the powerful Eladrin wizards to fight the Shadar-kai.
Half-Orcs are interesting because I placed them as the native species of The Land Between, however they lost everything, even the name of their race, when the Shadar-kai enslaved them. The Half-Orcs become the base stock that the Shadar-kai used for experiments. From them the Orcs, Goblinoids, and even stranger things came about. With their true name lost the remaining Half-Orcs are only know by their relationship to Orcs.
When the Shadar-kai originally created the contagious disease Lycanthropy they weren’t able to control the creatures it created. However with their studies of Lycanthropy they eventually created a more predictable strain of the disease which created the first Shifters. While this strain isn’t normally contagious Shifters do pass it on to their children.
While the story for Tieflings isn’t directly related to the Eladrin or the Shadar-kai they are connected to the third great power, Demon. When a person become a Magus it occasionally changes their body, in the most extreme cases they become something else entirely, a Tiefling.
I struggled a long time about what I wanted to do with humans. I didn’t want them to be just humans. I wanted them to have a place and a story like the other races. I stumbled upon the solution when I was figuring out why there weren’t Gods in the campaign. I eventually decided that Gods and their Angels did once exist in The Land Between, however when the tried to stop the war between the Eladrin and the Shadar-kai, the Eladrin built magical stairways into the sky and slew the Gods. The surviving Angels had their wings hewn off and were banished to The Land Between. These Angels became the first humans.
I still haven’t found a place for Dragonborn, Elves, Half-Elves, Halflings, or Dwarves but I am considering leaving some of them out entirely.