He became a U.S. citizen and during the Second World War he worked for the Office of Strategic Services as special assistant to the chief of its Research and Analysis Branch, William L.
[2] Several specialists of German and European history in America, including Peter Gay, were students of Holborn.
Their son, Fred Holborn (born 1928), was a senior adjunct professor of American Foreign Policy at the School of Advanced International Studies at Johns Hopkins University before his death in 2005.
[citation needed] Their daughter, Hanna Holborn Gray (born 1930), is a historian of political thought in the Renaissance and Reformation.
Other works by Holborn include the History of Modern Germany series, spanning three volumes and covering a four-century period from the Reformation and culminating in the capitulation of Hitler's regime in 1945.