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Regarding the celebration by the USC Center on Public Diplomacy of its tenth + anniversary, "Global Leadership in Public Diplomacy," nearly coinciding with the coinage of the term in 1967 by Dean Edmund Gullion of the Fletcher School of Law and Diplomacy (he also was a U.S. ambassador), let me point out that 1917 -- nearly a hundred years ago -- was the year of the founding of the United States Committee on Public Information, the George Creel Committee (1917-1919), arguably America's first "public diplomacy" (some would say propaganda) agency.
Re the Gullion term "public diplomacy," see Robert F. Delaney and John S. Gibson, editors, American Public Diplomacy: The Perspective of Fifty Years, The Lincoln Filene Center for Citizenship and Public Affairs (1967), in Gullion which writes (p. 31):
Even beyond the organ of the Government set up to handle information about the United States and to explain our policies, what is important today is the interaction of groups, peoples, and cultures beyond national borders, influencing the way groups and peoples in other countries think about foreign affairs, react to our policies, and affect the policies of their respective governments.
To connote this activity, we at the Fletcher School tried to find a name. I would have liked to call it “propaganda.” It seemed like the nearest thing in the pure interpretation of the word to what we were doing. But “propaganda” has always a pejorative connotation in this country. To describe the whole range of communications, information, and propaganda, we hit upon “public diplomacy” [my emphasis].See also John Brown, "Blast from the Past: An Addendum to Nicholas Cull's "'Public Diplomacy' Before Gullion," Notes and Essays Blog (September 28, 2015); "The Anti-Propaganda Tradition in the United States," Public Diplomacy Alumni Association (Created: 4 July 2003; Updated: 22 June 2008).
Walter Roberts, a distinguished, deceased -- sad news to all his admirers -- American diplomat, suggested in an e-mail to me some years ago that the term "public diplomacy" was actually coined before Gullion, i.e., in the post-WWII era before the 1960s. Having changed e-mail accounts (from hotmail to gmail) I regrettably did not keep a copy of Roberts's email, but perhaps a copy can be found in his archives (if they are being kept). Or if he expressed this thought to anyone else, please let me know.
On public diplomacy having become a "global phenomenon (rather than 'global leadership,' " see [a], as well as a series of articles in [b]).