In 1975, he published a study in the Harvard International Law Journal, questioning the legality of the expulsion of possibly as many as 15 million Germans from their homes after World War II, invoking the Atlantic Charter, the Hague Conventions, and the Nuremberg Principles. The article was followed by the book Nemesis at Potsdam (Routledge und Kegan Paul, 1977) which focused on the degree of responsibility of the British and Americans for decisions leading to the expulsions of these ethnic Germans. In the same year, an enlarged German edition was published by the legal publisher C. H. Beck, becoming a bestseller. In this book, Zayas took an interdisciplinary approach to the phenomenon of "population transfers" and examined the situation of the ethnic Germans from both a historical and legal perspective.

De Zayas was reportedly the first American historian to address this topic. [More]