Everywhere, the Great War precipitated a cultural paralysis the like of which had not been known since medieval times. The causes of this precipitate ice age are elusive. Its consequences endure. A pattern of cultural response and expectation in wartime was set for the next world war and beyond—to Korea, Vietnam and Iraq.
The freeze was the more remarkable since it followed hard upon the breakthrough to Modernism. In the Parisian decade before the outbreak of war, Pablo Picasso had gone successively blue, pink and Cubist; Debussy had perfected a form of musical Impressionism; Guillaume Apollinaire invented Surrealism.
I think a lot of it was the shock that a war could happen at all, and that it was so destructive to culture in a larger sense.