[Kristoffer O]

Fomoria and Tir na n'Og were the two nations that lived in the land before the age of men. The lore of the Tuatha had much more influence on Man than the Fomorians, but some of the magic of the giants can still be found in the realm.

The death summons are just residual knowledge from the Fomorian lore. The Fomorians used death magic before men came to the land. ME Man rarely use it, but some judges of LE Man might.