I forgot to write a faction until this morning, apparently, so this one will be quick.
The Sages of Twilight are a mysterious organization that collects only lore related to ancient civilizations. They seem particularly interested in societies that collapsed suddenly and violently. Perhaps they seek knowledge of what toppled them.
The Sages number perhaps a dozen high-level spellcasters scattered throughout the major cities of the world. They use permanent scrying spells and crystal balls to communicate and coordinate between themselves and their benefactors. As to the latter: While few people have both money and interest in these lost civilizations, those that do have little choice but to pay the Sages dearly for the information.
As a friendly faction, the Sages of Twilight are simply specialized historians and ideal quest givers, paying adventurers to delve into old ruins for lost books and relics.
As a foe faction, the Sages have an ulterior motive: they find the magical knowledge and artifacts that destroyed those ancient civilizations and sell them to the highest bidder. They are effectively trying to find arcane weapons of mass destruction and become the brokers for these weapons. If some group is trying to take over the world, they often employ the Sages. Stop the Sages, and save the world.