This race comes from the Shield region. In ages past, a great catastrophe destroyed their homeland, breaking it apart into islands. Before the disaster, they were known to be innovative artificers and warlords. Legends (or ghost stories) recount that their benevolent ruling council (made of 5 tieflings: 2 warlords, 2 artificers, 1 other) was destroyed by plague. So they sent messengers to every corner of Aelan, calling for entrants into a great magical competition. The winner would rule the tieflings into a new age of prosperity. The top wizards of many nations gathered together but were never seen again. None who witnessed the competition survived the catastrophe (at least no one admits they were there). Magical students in the area discovered the warlock way shortly afterward, although some believe it was no coincidence. Expeditions led by angry nations nearby found the tieflings that remained much changed, with their skin, horns and tail. Many were destroyed in the one sided war that followed as surrounding nations decimated their population.
Now, the story is still told in some areas but tieflings can be seen roaming the world. The Shield region is now group of islands known as the Shards. The tiefling race has no known major city, while small enclaves of dot the Shards.