In order to answer the question on how I build a fantasy world in an established time period, I have to go back in my writing career to the second novel I wrote, which was a straight historical fantasy. I spent months researching the Victorian era, and I had a lot of fun writing MY UNFAIR LADY. However, the entire time I was writing the novel, I kept asking myself, “What if?” What if magic, and not gender, was the basis for inheriting aristocratic titles? What if there were those who might be immune to the magic, being magical creatures themselves? I then had to go farther back into history to create the basis for the creation of my magical world, which was Merlin’s bloodline.
So, I started with my research into the time period before I ventured to add magic to alter it.
For my new series, THE ELVEN LORDS, I did the same thing; going farther back into history than the time period I knew I would be writing in. I established the basis for my magical world during the invasion of England by William the Conqueror. Instead of unifying England under one rule, my seven elven lords breeched the barrier between their world and ours and created seven sovereignties based on their own magical strength: Black for Mor'ded who rules fire, Blue for Breden who rules sea and sky, Green for Mi'cal who rules the forests, Gold for Roden who is master of glamour and illusion, Silver for Lan'dor who masters the blade, Brown for Annanor who rules the earth, and Violet for La'laylia who enspells gems.
My heroes and heroines became half-breeds, inheriting the beauty and magic of the elven lords, but with a human heart as well. So powers not only differed from realm to realm, but from person to person. I have posted my personal notes on the series on my website, if anyone would like to explore further into how I do my world building.
I think it can be more difficult and time-consuming to base a fantasy world in a historical backdrop, due to the amount of research it requires. It’s easier to create an entirely new world and make up the clothing, social mores, etc. But for me, it’s so much more satisfying to delve into the pageantry of historical eras because it’s a world I long to visit myself. Even if I do alter it with magic.
And one final note: the nice thing about adding magic to my world is that I can alter it to suit my modern sensibilities. For example, the elven lords brought bathing to England with them. I still reference that many consider bathing unhealthy, but in THE THE LADY OF THE STORM, my hero and heroines are clean. :}
By combining historical and fantasy, I have the best of both worlds.