The three-fold law, states that any good that a person does to another returns to themselves, magnified three times. Any harm also returns in the same ratio.
Before the persecution, witches, warlocks, and humans all lived in harmony. Humans sought out them for healing purposes during the Grey Plague. And as time went on, witches and warlocks were called on for many more purposes.
Even the king himself, who ruled over the fellow humans. He married a powerful witch, one who was said to raise the dead. Little did he know, she only wanted one thing from him, and it wasn't love. About a month after their wedding, the witch had hexed her newlywedded husband.
Three days later, the king passed from a sudden illness. And many believed his wicked wife had done it all for power. The witch queen was the first to perish before the following events led to the purge of witches and warlocks.
After some time the humans found that there was an underground city beneath where they settled. From that point on, anyone who practiced magic, or possessed powers was moved underground.
And while the city above thrived and advanced their technologies, the underground city remained behind, only gaining the surface's new technology through recycled items. But even still the price was high to upgrade. Let alone reach the surface again.
So how can a few young Wiccans change the minds of humans who can only see them as one thing? Evil.