Kosok began as an assistant professor of history at Long Island University (LIU) in Brooklyn, where he taught several courses in history. His work, "Modern Germany: A Study of Conflicting Loyalties," (1933), was written before the Nazis came to power and published by the University of Chicago Press as part of its "Studies of the Making of Citizens". One reviewer describe this as a "series on civic training in various countries and systems". Kosok's book was used by the State Department and others in training and preparing individuals for foreign service. It was reprinted in 1969.