Based on this experience, his subsequent 25-year career was as a leading scholar of the U.S. diplomatic history of the World War II period.
From 1922 to 1927, he was also an adviser on the American economy to the International Labor Office (ILO) of the League of Nations, in Geneva, Switzerland.
As World War II approached, he chaired the government's Interdepartmental Committee to Stockpile Strategic and Critical Raw Materials.
He had access to secret documents as well as his own memories to trace the convoluted course that Washington followed in abandoning its traditional isolationism for a policy of global intervention.
However, scholarship since the 1980s has largely vindicated his interpretation of the use of nuclear weapons in 1945 as an effort to end the bloodshed as fast as possible.