It is the emergence of mass media which makes possible the use of propaganda techniques on a societal scale.
Recent Research and Scholarship on Propaganda
Renee Hobbs and the Media Education Lab team have published two articles (so far) about teaching about propaganda:
Hobbs, R. & McGee, S. (2014). Teaching about propaganda: An examination of the historical roots of media literacy. Journal of Media Literacy Education 6(2), 56 - 67.
Hobbs, R. (2013). The blurring of art, journalism and advocacy: Confronting 21st century propaganda in a world of online journalism. I/S: A Journal of Law and Policy for the Information Society 8(3), 625 - 638.