 After the implementation of the Anti-Semitic Italian Racial Laws in 1938 Sonne lost his post and emigrated to the United States by 1940.He became a professor of the Hebrew Union College in Cincinnati, where he died on 27 November 1960.Sonne published in four languages, English, German, Italian and Hebrew, on a wide range of subjects stretching from biography to rabbinics and philosophy, with his contribution to the "Wissenschaft des Judentums" on the subject of Renaissance history the most noted.