Read "Crystallizing Public Opinion" and "Propaganda" written by Edward Bernays to get a sense of how long TPTB have been fully coordinating the brainwashing of the masses. Those books were written in the 1920s and Bernays makes clear that a number of scientists and psychologists had definitively figured out the methods and mechanisms required to generate "GroupThink", which was the great breakthrough around the turn of the 20th century.

Prior to the 20th century, the best "propagandists" could do was to reinforce existing beliefs and play on stereotypes. Bernays and his ilk figured out how to generate new "beliefs" within the safety and security of one's chosen mainstream group/institution/belief-system.

A cursory search on Bernays will reveal he worked for a wide variety of corporations and commercial operations to help them sell their products. However, a deeper search reveals he also worked for the war (defense) department during WWI & WWII, the OSS, CIA, FBI, State Department as well as other political lobbying firms as well.

So I'd say 120 years is about right. This timeline dovetails with William Randolph Hearst's complete takeover and ownership of almost all the biggest newspapers in the Unites States as well.

The marriage of "coordinated news" and "science of GroupThink" opened the doors for the "belief-shapers" to mislead the masses into all the catastrophic shifts in opinion that have taken place ever since.