We often refer to a "conspiracy theory" of politics, where events are explained by people conspiring against other people. The term dates back to the 1950s, but interestingly around that time it was synonymous with a more colorful phrase: "devil theory". The above quote is from a Jun 21 1964 article in the Winoda Daily News titled "Barry Sets Up Scapegoat" about how Barry Goldwater was already floating conspiracy (or "devil") theories about his inevitable failure to become president.
The "devil" here is not literally Satan or some supernatural being, but instead refers to some organization or group. With Goldwater it was "the Eastern establishment" or "the Eastern conspiracy". This echos more modern usages, like "a vast right wing conspiracy," or "the Deep State."
Another 1964 usage is from the book Contemporary Theory in International Relations, by Stanley Hoffman (Ed).
Again this is described as looking for scapegoats, someone to blame. Also note the reference to the "influence of the munitions makers" - A reference to the military industrial complex.
The origin of the phrse revolved around the book The Devil Theory of War: An Inquiry into the Nature of History and the Possibility of Keeping Out of War, by Charles A. Beard, 1936. His book is essentially a rejection of the devil/conspiracy theory of history
The phrase might have roots in "The Devil Theory of Disease" as described in this 1916 article:
A rather odd article, seeming saying the germ theory of disease is like the devil theory, but it does reflect the sentiment of blaming ones ills on a scapegoat, and not taking "personal responsibility" (which the writer there feels means good diet and hygiene).
The New Yorker in 1925 has an interesting snippet on the "devil theory of lobbying"
A similar phrase is the "devil theory of economics", which refers to a belief in evil forces or some other prime mover causing economic harm (as opposed to market forces). Again personal responsibility is emphasized, like in the 1952 version.
An even more removed usage comes from the 1872 History of Salem Witchcraft, where the author describes the "devil theory" (of the movement of a planchette on a OuiJa board) as lacking science (but does not really come up with a good alternative.)
Coming back to more modern usages, in the 1941 short story Logic of Empire by Robert A. Heinlein, the character "Doc" describes the "devil theory" as a fallacy, saying "You have attributed conditions to villainy that simply result from stupidity" (a form of "Hanlon's Razor")
In the 1970 article Devil Theories of U.S. Foreign Policy, Ernest W. Lefever does not limit the "devil theory" simply to conspiracies, but characterizes it as a search for a simple answer, a single flaw in a complex world.
Later he rather brutally criticizes the book "The Power Elite, the CIA and the Struggle for Minds" by G. William Domhoff
More recently again, the term "devil theory" was used synonymously with "conspiracy theory", and contrasted with incompetence, in the 1987 NSA article, "Every Cryptologist Should Know About Pearl Harbor "