"If we understand mechanisms of the group we can control and manipulate the will of the masses without their knowing it"
You can learn a little bit more about Bernays in this NPR piece "Freud's Nephew and the Origins of Public Relations." which tells the story of Bernays being hired by the Beechnut packaging company in the mid 1920's to improve sales of bacon, it's primary product.
Bernays asked Doctors if they favored a "light" breakfast or a "hearty" one. Doctors favored a hearty breakfast. Bernays then equated bacon with a hearty breakfast and created an ad campaign which promoted bacon and eggs as a breakfast recommended by Doctors and therefore associated with a feeling of well being and good health. He also sold the American people on Ivory Soap, Lucky Strike Cigarettes and oddly enough ballet and dance.
The enlightenment way of looking at the world recognizes there is a reality and we need to understand it through reason and rational thought. It was believed that people are rational beings and if you present a well orchestrated case you can persuade them.
Freud believed that people aren't rational at all but were rather driven by unconscious desires and visceral impulse - sex, agression, security, self preservation. Edward Bernays took Freud's ideas and created the new field of public relations in the 1920's....the world of advertising and what we now call spin in the political arena was changed forever.