I think the go-to essay for understanding the history conspiracies and conspiracy theories is Richard Hofstadter's "The Paranoid Style in American Politics," which you can find here. To quote myself from a previous answer:

[w]hen in graduate school, I was a teaching assistant in a course called "Conspiracies and Conspiracy Theories in U.S. History and Politics).

... Hofstadter's argument revolves around the idea that "angry minds" in politics have read personal or other uninvolved motives into the political or religious other over time. He covers early paranoia against the Illuminati, Jesuits, and Masons before moving into the time of his essay (the Goldwater campaign).

Moving from that, Robert Alan Goldberg's "Enemies Within" is a good overview of post-WWII conspiracy theories (UFOs, Kennedy, etc.)

We also read Peter Charles Hoffer's "The Devil's Disciples: The Makers of the Salem Witchcraft Trials," in which he argues that the Salem trials were early examples of paranoia (over social and economic outliers and change).

Here's the course website (apologies for the Geocities-esque look and feel) if it's helpful: http://www.pasleybrothers.com/conspiracy/

I am not sure how to understand the question. Are you asking if there was something that made people start to think their goverment was making stuff up ... or are you asking about actual "false flag" operations, like the Gulf of Tonkin incident?