Most of the creatures in the Sidhe Empire are humans.
In our fantasy realm, the queen of the elves saw the fall of the Aesir and withdrawal of the Vanir as an opportunity; she refused to fade …instead she made her peace with this change in humankind’s fortunes and harnessed us to serve her.
This is why the empire remains in the mechanical age of steam. Humankind, by entering into a vassal system with the fae received benefits (long life, a certain freedom from disease), but our science and technology is stagnant. Rather than harnessing the power of the atom, these people have learned to use magic …even to go so far as capturing the souls of men or the spirits of elfish prisoners to power their machines. There are no star-ships, but portals that link the worlds. No nuclear reactors to fill the cities with light, but golden spherical prisons beneath her cathedrals where supernaturals are milked for their innate power. For that is what humankind does …we use the resources of our environment to serve our needs; but here …in this place …our fecundity is held in check by a nature that knowingly uses us.
Humankind is her army, pouring forth through portals opened to conquer world after world in her name. We are legion, but we are also leashed. As for the supernaturals themselves? Some are renegade, but most serve willingly …for she is fierce and beautiful, and when she is delighted her magic fills them with joy.