After witnessing violent antisemitism in Danzig along with the Nazi expulsion of Jewish students from local schools, his parents sent him to study in Paris.
[8][2] When it became too dangerous for Rosenberg to stay in Paris, he moved south, ending up in Marseille, having followed Miriam Davenport there when she recruited him to join Varian Fry's Emergency Rescue Committee, a network formed to extract artists and intellectuals from Vichy France.
[2] After Fry's network had to shut down its activities in France (it later became part of the International Rescue Committee), Rosenberg was picked up for transport to a camp in Poland but managed to escape and join the French Resistance.
In 2017 the French ambassador to the United States personally made Rosenberg a Commandeur in the Légion d’Honneur, among France’s highest decorations, for his heroism during World War II.
[13] His linguistic skills led to teaching language courses in French, German, Russian, Yiddish, and Polish at Swarthmore as well as Bard.
"[2] After his retirement, he continued teaching, broadening his subject matter to include modern literature from Africa, the Middle East, India, and Asia; at The New School he taught a weekly course in political and cultural history.