Complex sentence: In the fictional setting of the story, fairies and their other magical cousins used to live above ground but when the human race evolved, the fairies were forced to move into more secluded places then, finally, underground.
Split into simpler sentences: In the fictional setting of the story, fairies and their other magical cousins used to live above ground. When the human race evolved, the fairies were forced to move into more secluded places then, finally, underground.