At the end of the final human-elven war, the elves' greatest mages were assembled to put an end to the conflict once and for all. Together, they cast a powerful shrinking curse that reduced all humans to near-insignificance overnight, thus beginning the Age of Elves.
In the days to come, countless humans would be killed by the elves, with everyone from soldiers to vengeful widows and even unsuspecting children taking part in the massacre. Every human that could be found was exterminated.
For centuries, humans were believed extinct. It wasn't until the year 813 AE that elven biologists discovered surviving human populations leading an ant-like existence deep in the wilds far from all civilization.
The discovery caused a stir in elven society, and tens of thousands traveled to see for themselves that once-proud race which had so troubled their kind in ages past. Some took to crushing whatever humans they came across, whether as revenge for some ancestor killed in the wars or simply for the fun of it. Others had a different idea and abducted whole populations of humans, bringing them home to keep as symbols of their race's absolute victory over their ancient enemy.
For a time the adoption of humans as pets or toys became something of a fad. At its height of popularity there was hardly an elven household that didn't host at least one human town, but that would all come to an end in a few decades as humans came to be regarded as terrible pests. With their increased fertility rate and accelerated life-cycle, humans could infest an entire household in as little as a year, provided the initial population managed to survive long enough to breed, and from there they spread to neighboring houses like a wildfire, outcompeting other pests like ants or termites.
Small as they were, they easily went unnoticed until well established, living on crumbs and scraps left in the trash, but once their numbers ballooned far enough, they started targeting fresher foods. By the time the elves started noticing the missing produce, it was already too late; the humans had fully established themselves in the house and doing away with them was near impossible.
By 860 AE, public opinion had turned decidedly against the humans. Those pet towns and cities that elves had lorded over for decades were all crushed or drowned by their masters, though it did nothing to stop the problem. Edicts saying that all humans were to be killed on sight proved nearly useless as humans had a knack for avoiding notice, thanks in no small part to their cunning and near-microscopic size.
Proposals that magic be once more wielded against the humans proved to be a pipe dream also, as the magical knowledge that let the elves emerge victorious in the great war had long since been forgotten in favor of a more technological approach, at least among the city-elves. “Wild” elves still retained some of that knowledge, and for a time the city elves believed that was why humans weren't as much of an issue for their “uncivilized” cousins.
The assumption turned out to be mistaken; it was the fairies, not the elves, who were keeping the human populations under control as the humans' greatest natural predator.
Once treated as another pest by the city elves and chased out by force, fairies were now welcome back as the one thing capable of solving the human problem. For weeks the mischievous critters flooded into each city to feast on the seemingly endless supply of humans, coming in such numbers that at first it seemed the elves had merely replaced one pest with another. By the end of the first month, however, the human population stood much reduced and the fairies began to leave of their own accord, as few of them had any liking for the cities anyway.
At last the elves could breathe easy and their lives go back to normal. And though human populations would eventually recover, as long as fairies were allowed to remain they would never again trouble the cities to the same degree, becoming just another troublesome but manageable pest trying to survive in a world shaped by their superiors.