Nitobe was a prolific writer. He published many scholarly books as well as books for general readers. He also contributed hundreds of articles to popular magazines and newspapers. Nitobe, however, is perhaps most famous in the west for his work Bushido: The Soul of Japan (1900), which was one of the first major works on samurai ethics and Japanese culture written originally in English for Western readers (The book was subsequently translated into Japanese and many other languages).
When the League of Nations was established in 1920, Nitobe became one of the Under-Secretaries General of the League, and moved to Geneva, Switzerland. He became a founding director of the International Committee on Intellectual Cooperation (which later became UNESCO under the United Nations' mandate).