Tartarus

The so-called Tartarus is a huge and deep cave in the center of northern countries. It is also the name of a self-conscious liquid that is used as a weapon by Satanists.

Background
Whenever a war broke out, because it was very problematic to bury a corpse, some countries threw all the corpses into this deep cave. In addition, occasionally there was an unknown liquid pouring out of this deep cave also named Tartarus, it has the power to drain sacred and holy powers being the natural enemy of the worshipers of the Great Light and the Angels.

If the countries are going to make cemeteries one by one, the resources probably will not be enough. If there is a cave that can swallow everything clean, then wartime people will naturally have the idea of "To avoid problems, just throw everything in" and save resources to keep fighting.

Trivia

 * Tartarus it is also known as Hades, Naraku or Hell depending on the translation.
 * All names refer to the world of the dead