One of his most influential books, "The Deluge" (1965), dealt with the transformations in British society brought about by the First World War. Its main thesis was that the war had brought about positive and lasting social changes (in the rôle of women, in the acceptability of state intervention for social reasons, and so on). Despite its terrible tragedies, Marwick believed that the sum result of the war was that Britain was a better place to live in the 1920s than in the period before the war.