Jesse Walker's superb analysis of American paranoia and fear, The United States of Paranoia, covers al-Qaeda, the Illuminati, and everything in between. Here, he lays out five conspiracy theories.

Conspiracy theories are not a recent invention, and their appeal has never been limited to the fringe. Since colonial times, Americans across the political spectrum have been haunted by tales of hidden hands and secret plots. And even when those stories are false, they have truths to tell us. A theory that catches on may say nothing true about its ostensible subject, but it still says something about the anxieties and experiences of the people who believe it.

Here are five American conspiracy stories that have found a following at some point in the last four centuries. We'll start with the most absurdly inaccurate of the five, then move gradually toward empirical accuracy.

Theory #1: Native Americans are minions of Satan. The English theologian Joseph Mede believed that the devil settled the New World before the Christian colonists got here, recruiting "some of those barbarous Nations dwelling upon the Northern Ocean" and promising them "a Countrey far better than their own." Some of the leading Puritans took up this idea and ran with it. William Hubbard, an influential clergyman, believed hostile tribes were controlled by Satan—in Hubbard's words, "actuated by the Angel of the bottomless pit." After the Salem witch trials, another prominent minister—Cotton Mather—suggested that the alleged spiritual attacks originated "among the Indians, whose chief sagamores are well known unto some of our captives to have been horrid sorcerers."

Theory #2: A southern cabal killed presidents Harrison, Taylor, and Lincoln, and it tried to kill presidents Jackson and Buchanan. In 1864, John Smith Dye's book The Adder's Den described a series of plots that read like a 1970s conspiracy thriller set in the antebellum era. Dye blamed an 1835 attempt to shoot President Andrew Jackson on former vice president John Calhoun, though the author left it open whether Calhoun had actually hired the assassin or had just incited him. Dye was less ambiguous about the rest of his narrative, claiming that William Henry Harrison and Zachary Taylor had been poisoned for opposing the slave states' agenda and that an attempted poisoning had intimidated James Buchanan into becoming "the tool of the slave power." When a second edition of the book came out after Abraham Lincoln's assassination, Dye naturally added Abe to the list of victims.

You won't find much credible evidence for Dye's charges. But he didn't dream them up by himself either: He drew on rumors that had been floating through Whig and Republican circles for years.

Theory #3: White doctors are conducting covert experiments on blacks. In the 19th and 20th centuries, rumors in African-American communities held that "night doctors" would capture blacks, kill them, and dissect their corpses. Sometimes scientists were said to use the bodies' blood to make medicine. During the Atlanta child murders of 1979 to 1981, when at least 21 black children and teenagers were kidnapped and killed, a particularly gruesome version of the tale held that the government was harvesting the kids' genitals to make aphrodisiacs.

Such stories are often obviously false. It's hard to dismiss the entire genre, though. In the antebellum South, according to the medical historian Todd Savitt, scientists really did take "advantage of the slaves' helplessness to utilize them in demonstrations, autopsies, dissections, and experiments." The abolition of slavery didn't end the abuses. In the Tuskegee experiment of 1932 to 1972, the federal Public Health Service offered free medical care to several hundred black sharecroppers. It didn't tell the patients that they had syphilis, which the doctors deliberately left untreated in order to study whether the disease affects blacks and whites in different ways.

Theory #4: Working in secret, a conspiracy replaced the country's original constitution with a document that concentrated more power in the national government. The Constitutional Convention was originally supposed to revise the Articles of Confederation, not replace it entirely. So imagine the average American's surprise when a dissenting delegate to the convention, Luther Martin, gave a long address to the Maryland House of Delegates. A cabal, Martin warned, was "covertly endeavouring" to "abolish and annihilate all State governments, and to bring forward one general government, over this extensive continent, of a monarchical nature."

Martin's charges were obviously over the top. But when his fellow Anti-Federalists, such as Abraham Yates, argued that the pro-Constitution forces had "turned a Convention into a Conspiracy," there was a core of truth to the charge; it's just the spin they put on it that sounds strange today. The Constitutional Convention did meet in secret, refusing even to publicize the minutes of its debates. It did exceed its original mission, and some of the delegates did intend from the beginning to overshoot those instructions. There is even evidence of irregularities in the state-level votes to ratify the Constitution. If ratification is not usually described in conspiratorial terms today, it isn't because there is any serious dispute over those facts. It's because most modern Americans are glad the Constitution became law, and thus are unlikely to think of its genesis in those terms.

Theory #5: The U.S. government deliberately undermined protest movements in the 1960s. If you were politically active in the 1960s—in the anti-war movement, say, or the Black Panthers—you may have suspected the Federal Bureau of Investigation of spying on your group. And you may well have been right about that, though you weren't necessarily right about who the spy was. Under the program known as COINTELPRO, FBI agents didn't just infiltrate and disrupt dissident groups. They made sure the groups knew that they were being infiltrated and disrupted, so activists would suspect one another of being police agents. In effect, COINTELPRO functioned as a conspiracy to defeat subversive conspiracies by convincing the alleged subversives that they were being conspired against.

It is a deeply paranoid story. It is also demonstrably true, with many pages of the Senate's Church Committee report dedicated to exposing it. As the old saw goes, just because you're paranoid doesn't mean they aren't out to get you.