The revolt of unreason was a revolt against modernity itself. It held the idea of an ancient and immutable essence of man against the unstable identities of city folk, it articulated itself in the male backlash against early feminism, in violence and the cult of manliness, in reactionary politics. But it was not backward-looking in all its aspects: it also played an important role in Futurism, avant-garde art, and 'scientific' racial theories, in mysticism, and in the careers of men as different as W.B. Yeats, James Joyce, Adolf Hitler and Mark Rothko. The cult of unreason was important to movements as seemingly incompatbible as abstract modernism and fascism.
The years leading up to the Great War were (of course) much more than a belle epoque, after which the lights went out all over Europe -- once again.