This is, of course, the Age of the Fae; but why? The Age of Elves was ruled by elf-kind, and the Age of Men was ruled by humans; the Age of the Beastmen was full of the nasty brutes. But the Fae do not seem to be quite as well-heard of; their place in stories is mysteriously absent.
The Fae, or Faerie-folk, are not an outgoing people. They are sly, and wild, and ethereal. Unlike the solid elves or brash humans or brutish beastmen, the Fae would rather sit back and manipulate, pulling strings in the shadows. They are wild, and yet there is a method to their madness; all Fae are bound by an extraordinary set of rules. The rules bind and free; they are loved, and hated, and all faerie-kind know them intrinsically. Fae hate iron, and cannot bear to wear it; likewise, if asked a question three times, they must answer truthfully the third time. Their promises have permanent bonds; a promise must be carried out, though admittedly only the word, not the intent.
Before I get too far, I would like to quash your idea of faeries. As you read this, your mind is conjuring images of tiny, brightly-colored forest dwellers. While that may describe one kind of Fae (namely, the pixie), it hardly does justice to the others.
There are Sylphs, who like to call themselves elves; tall and slender, witty and flowery, yet as unmoving as mountains, the sylphs are as dangerous as they are beautiful. Then there are the naiads and dryads, spirits of water and trees; they are seductive and playful, though selfish; beware being called their friend, for you may end up living with them forever. Pixies, Fairies, and Sprites are small, winged creatures, playful and childlike. Brownies are similar to Pixies, but have no wings. Green men, too; they are tall humanoids, quite and watchful protectors of the forests that shun contact with others. Leprechauns are Faerie-kind, too; greedy beings who can leap huge heights at will, and often lay in wait to steal from travelers. Not all Fae are beautiful, however. Great, hulking trolls are Fae as well, and the horrid Throghrin, powerful hybrids with a ghoul's touch. And then there are the black unicorns... A black unicorn is a sick mockery of a horse, as if made by someone who had only heard a poor description. It's eyes are bloodshot and bulging, and its skin is covered with a black carapace. Its tail is a fleshy, mottled lump. On its forehead, between its eyes, is a black, twisted horn, and its whinny, if it can even be called that, is a shrill woman's scream; its mouth is filled with cat-like teeth. They are no relation to the white unicorns of legend.
The Fae, as I said, prefer to stay out of sight, but their presence has been unmistakably felt. Magic thought lost has been rejuvenated; wild, ancient magic, of dark woods and ruined shrines, of wolf-weres and speaking snakes. The Fae have awoken the deep magic of the earth, nudging it out of its slumber, and unleashing it upon the unsuspecting civilized world. For hundreds of years, the plans of the Fae have matured, and only now are those plans coming to light. Spies for the Fae - and even the Fae themselves - walk through human cities, wheedling and eavesdropping, amassing power to topple empires. They reward the schemers and plotters, and undermine the wealthy and powerful.
Plots have recently been discovered and thwarted, but many more lurk beneath the surface, threatening to topple empires even as ancient and powerful as Mareten. And all of this - what do the Fae stand to gain? Little, if anything; like most machinations of Faerie-kind, it is all on a whim. Take my word for it; the Age of the Fae will end, not with war, not with old age, but with a whispered sigh: "I'm bored."
The elves and men and dwarves can be reasoned with, and the beastmen defeated in combat, but to best the Fae, one must be willing to face the fancies of a child.