This guy is actually fairly ignorant of the history. The Illuminatus! Trilogy was a parody of conspiracy literature and was released in 1975. There were hundreds of books about the freemasons and the illuminati going back to the 18th century. There was a whole anti-Masonic political party in the United States in the 19th century. In particular, the book parodied the John Birch society.

The real innovation in the book was how freely they mixed and matched conspiracy theories from the left and right to turn them into a gigantic ur-conspiracy.