Clute has a section in The Encyclopedia of Fantasy on the significance of WWI
Many authors who were in the trenches, or significantly affected, wrote "aftermath societies" -- Tolkien, Hugh Lofting, C. Lewis, E. Eddison, A. Milne, E. Wyke-Smith, David Lindsay, RobertNichols, E. Shepherd,...
Arguably they all responded in a broadly similar way to WWI -- clear sense that something had gone seriously wrong -- fantasy as a counter-narrative when treated seriously