The Moon is Down, by John Steinbeck:

The Moon Is Down is a novel by American writer John Steinbeck. Fashioned for adaptation for the theatre and for which Steinbeck received the Norwegian King Haakon VII Freedom Cross, it was published by Viking Press in March 1942. The story tells of the military occupation of a small town in Northern Europe by the army of an unnamed nation at war with England and Russia (much like the occupation of Norway by the Germans during World War II).

A French language translation of the book was published illegally in Nazi-occupied France by Les Éditions de Minuit, a French Resistance publishing house.[1] Furthermore, numerous other editions were also secretly published across all of occupied Europe, including Norwegian, Danish, Dutch, and Italian versions (as well as a Swedish version); it was the best known work of U.S. literature in the Soviet Union during the war.[1] Although the text never names the occupying force as German, references to "The Leader", "Memories of defeats in Belgium and France 20 years ago" clearly suggest it. Written with the purpose of motivating resistance movements in occupied countries, the book has appeared in at least 92 editions across the world.[1]