Wraith: The Great War is the lone historical supplement for Wraith: The Oblivion. It details the chaos in the Underworld caused by the bloodshed in World War I and the subsequent Great Maelstrom that resulted.
Although the book starts because of the Great War in the Skinlands, especially the British push on the Somme River battlefront, the real war the title refers to is the attempted coup d'etat by the Smiling Lord and the resulting struggle between Legions for power and stability that adds to the already powerful chaos of the Maelstrom. The Legions, Heretics, and Renegades divide themselves into factions supporting either the New Stygians, led by the Smiling Lord, or the Loyalists, led by the Skeletal Lord and the Laughing Lady. To complicate things, the Emperor of Stygia, Charon, has secluded himself in his home, the Onyx Tower and has not been seen or heard from for almost nine years.
There are few major similarities and differences between the structure of Wraith society in this and the original Wraith: The Oblivion society. The structure of the Hierarchy is firmly in place and changes little over the next century. The Guilds exist in their usual secretive forms, aiding the Legions who suit their goals the best. There are changes to several Arcanoi, most notably Inhabit which has become a more primitive form known as Kinesis.
There are also details on the non-European wraiths of war, most notably the recruits of India that die far from Swar, the forced military service of many from Africa that die away from the Dark Kingdom of Ivory, and the Japanese wraiths of the Yellow Springs who perished while taking advantage of the Great War to take over Manchuria.