Short answers, pulled from the story.
The earliest known use of the term conspiracy theory was by American author Charles Astor Bristed in a letter to the editor of The New York Times on the 11th of January 1863. He used it to describe claims that British aristocrats were deliberately weakening the United States during the Civil War. The Oxford English Dictionary's earliest citation is a 1909 article in The American Historical Review.
No. Michael Butter, a Professor of American Literary and Cultural History at the University of Tubingen, found that the CIA document most often cited as evidence of this uses the phrase conspiracy theories only once. Recorded use of the term dates to at least 1863, and it appeared in coverage of the 1881 shooting of President James Garfield, more than six decades before the CIA existed.
AIDS denialism by the government of South Africa, motivated by conspiracy theories, caused an estimated 330,000 deaths. Conspiracy theories about genetically modified foods led Zambia to reject food aid while 3 million people suffered from hunger. QAnon and denial of the 2020 United States presidential election results led to the January 6th Capitol attack. Conspiracy theorists Timothy McVeigh, Anders Breivik, and Brenton Tarrant each used conspiracy beliefs to justify mass violence.
Conspiracy theories use circular reasoning: both evidence against the theory and the absence of evidence for it are reinterpreted as proof that the cover-up is working. Psychologist Stephan Lewandowsky observed that the stronger the evidence against a conspiracy, the more believers conclude that conspirators must want people to accept the refutation. This self-sealing quality, which researchers call epistemic self-insulation, makes the theories resistant to external correction.
Researchers identify three categories of motive: epistemic (desire for certainty), existential (need for control and safety), and social (desire to feel part of a knowing group). Belief is correlated with psychological projection, paranoia, and low feelings of political efficacy. A 2020 review found that most cognitive scientists consider conspiracy theorizing typically nonpathological, arising from common human tendencies toward gossip, group cohesion, and a search for meaning.
For the general public, encouraging analytical thinking and prebunking, informing people in advance about misleading information and why it should be rejected, have shown consistent effectiveness. Penn State researchers found that short videos explaining concepts like correlation and causation reduced conspiracy endorsement among more than 2,700 participants. A 2020 review found that the backfire effect, in which refuting misinformation reinforces it, rarely occurs in practice, meaning factual corrections generally have a positive impact.