Military action
The period of time when Nordea the Blood Witch attempted to destroy Arheim to gain magical power.
Over a period of sixteen years, a powerful necromancer and witch called Nordea formed a secretive cult that promised salvation for the wicked. It called for blood sacrifice, in order to give Nordea the power to eclipse the gods and bless her followers. This is, at least, what she told those that joined the cult. In reality she was a woman mad with power and blood lust. She wanted to be stronger than everyone in existence, and she nearly got her wish. By having several covens under her command curse the land, she began to wither possible resistance away and siphon their abilities.
Once her plot was discovered by the world at large, which only happened because of a mistake of address that had information about the cult sent to the wrong place, the world mobilized, creating the Witch Hunt and destroying the cult over the course of several years. Even vampires plotted her death, going so far as to build a stronghold that could serve as a base for their spell casters so they could dismantle her curses. Nordea died during the final battle that included the most capable fighters in the Witch Hunt, including Hargrim the Blade Master, and her body was burned at the stake to ensure nothing remained of the powerful blood witch.
The war with Nordea caused superstition and fear to spread throughout Arheim that lasts to this day, and anything resembling witchcraft is brutally dealt with.