Necromancy and the Undead
In the scramble to rebuild after the Loss, people began to experiment with all sorts of arcane rituals. One promising avenue of magic involved harnessing power from the dead. It is unclear exactly how this worked, since officially, there are no records of the method used. In fact, it is unclear if necromancers have all independently discovered the same method, if they have all been taught by some mysterious benefactor, or if they have come across completely unrelated methods of raising the dead.
Congress Monastery and especially the Church of Lumen have led the charge in stomping out potential necromancers. This occasionally puts them at odds with churches who believe that communication with the dead is not inherently evil.