The best book I've read on WWI has to be Paul Fussel's The Great War and Modern Memory. Here's
Stephen Metcalf (in Slate), on Fussell:
" “I am saying,” he concludes one chapter in The Great War, as if replying to a margin note from a junior editor, “that there seems to be one dominating form of modern understanding; that it is essentially ironic; and that it originates largely in the application of mind and memory to the events of the Great War.”
Fussell iterates the thesis at length, and the result is a unique kind of masterpiece —a plausible argument by an ex-warrior in favor of literature as the most appropriate measure of the immense shock of not only war, but all social change..."