When a House stenographer was recently yanked out of the chamber for ranting about Freemasons, you could have figured out what she was talking about by a quick check of the index of this book.
It's by Jesse Walker, and it is an extremely entertaining history of popular American conspiracy theories. Which means it's a pretty good history of America generally. It takes off from Richard Hofstadter's 1964 famous article, "The Paranoid Style in American Politics", where it was argued that "angry minds" at the extreme fringes were wont to worry about various schemes being carried out behind the scenes, hidden from the general populace. Wake up, sheeple!
Except (as Jesse shows) in America, conspiracies aren't exactly fringe material at all; people from left, right, and center buy them, and it's been going on ever since colonial times.
President Obama, it should be remembered, darkly hinted about the "them" trying to "hijack" his agenda: "The American people deserve to know who’s trying to sway their elections, and you can’t stand by and let the special interests drown out the voices of the American people.” Continuing: It could be the oil industry, it could be the insurance industry, it could even be foreign-owned corporations. You don’t know because they don’t have to disclose. Now that’s not just a threat to Democrats, that’s a threat to our democracy.” Eek!
Now (it should be said) sometimes conspiracy theories aren't always bunk. (Although when Obama espouses them, it's a pretty good bet that they're cynically-constructed demagoguery for his low-information followers.) For example, there's the one where a small band of conspirators plotted to overthrow the established form of American government by hijacking a reform effort, replacing it with a totally new and more centralized scheme, and inventing a rule whereby the new system could be enacted under a relaxed standard.
Oh, wait: that's pretty much how the US Constitution happened.
Walker has a good taxonomy of paranoia: there are Enemies Outside, plotting outside the gates; Enemies Within, where you can't tell your innocent neighbors from the evil plotters; Enemies Above, where the elites at the top scheme against you; and Enemies Below, where the undertrodden are looking to take over. Finally, there's the "Benevolent Conspiracy", a "secret force working behind the scenes to improve people's lives." You know, like Google.
As I said: very entertaining, and you can learn stuff.