In the dark of the night of July 19, AD 64, a fire broke out in the slums of Rome and, swept along by vicious winds, devastated the town, leveling several districts entirely. The fire burned for six days, died down, was reignited, and burned for three more. Hundreds of people were killed; many more were left destitute and homeless.

In the midst of it all, the famously conniving Emperor Nero—who was away in his holiday home on a cool hillside when the fires began—was reported by the historian Tacitus to have placidly watched the city burn as he nonchalantly played his fiddle or plucked his lyre. (Tacitus was writing years later; he was a teenager when Nero died, and historians have argued since that we know little about his sources or biases.)

Per Tacitus, Roman citizens began to suspect that Nero himself had ordered the fires set, to consolidate his power and reconstruct Rome in the manner he saw fit. Or he had allowed the fires to keep burning for the same reason, even sending mobs to prevent citizens from quashing the flames. Nero, meanwhile, blamed the fires on an upstart religious group, the Christians, and used the pretext to merrily persecute and crucify them. Many parts of the story have been called into question by modern scholarship, but the Nero-fiddling-as-Rome-burns version is one of the earliest known examples of two things. First, it’s a conspiracy theory about the government unleashing chaos to extend control; second, a government official used a conspiracy theory to realize political ends.

All these many centuries later, conspiracy theories relating to September 11 echo the Roman fire incident: that the Bush administration either passively allowed the attacks to happen or orchestrated them for political ends. (The two branches of 9/11 conspiracism have become so entrenched that they have their own acronyms: LIHOP, for “let it happen on purpose,” and MIHOP, “made it happen on purpose.”)

The Rome fire myth also illustrates something else: people historically developed conspiracy theories about local phenomena, things that happened right in front of them. As our world has gotten larger and more connected, we tend to theorize about distant people, places, and events. Our theories are so broad they encompass the galaxy itself and the most distant reaches of space: UFO conspiracism has been a beloved American pastime for nearly a century.

The local element hasn’t disappeared, though; indeed, our communications have made conspiracism more intimate than ever. Social media allows us to fasten a conspiracy on a seemingly random or inconsequential person: the victim of a school shooting, say, or the owner of a pizza parlor. Self-appointed online detectives can use digital tools to contact, expose, harass, and occasionally terrorize the alleged plotters in ways that would have been impossible even twenty years ago.

Thus conspiracies have changed their form repeatedly over history, even in the relatively young history of the United States. A lot of conspiratorial hysterias in the early days of this country focused on what the historian Kathryn Olmsted in her book Real Enemies calls “alien subversion”: a fear that disaffected outside groups—Jews, Catholics, Freemasons, Mormons—were plotting to seize control for themselves. Sometimes, more rarely, the alien enemy was closer to home, as with the Salem witch trials, when a community turned on itself, neighbor accusing neighbor of serving the Devil in secret.

But as Olmsted points out, something significant changed in the twentieth century. Theories began to focus not on an outside, alien group seizing power, but on the existing power structure, the government itself; the Romans redirecting their attention back to Nero, as it were. “No longer were conspiracy theorists chiefly concerned that alien forces were plotting to capture the federal government,” she writes. “Instead, they proposed that the federal government itself was the conspirator. They feared the subversive potential of the swelling, secretive bureaucracies of the proto-national security state.” As the government grew larger, particularly its military element, the number of conspiratorial ideas about it expanded proportionally. And some of those suspicions weren’t unfounded: the country has innumerable examples of actual government conspiracies, which became more outlandish and horrifying as we approached the present day.

In 1954, the CIA directly assisted in overthrowing Guatemala’s president, Colonel Jacobo Árbenz Guzmán, in large part to protect the interests of the American-owned United Fruit Company. In 1973, the agency did the same in Chile, to destabilize and drive out of power Salvador Allende, the country’s democratically elected Socialist leader.

In the 1960s, the federal government engaged in systematic covert harassment of such activist groups as the Black Panthers and the American Indian Movement, and of Martin Luther King, Jr. and other members of the Southern Christian Leadership Conference, conspiring to ruin the lives of their leaders, set the membership against one another and against other activist groups with whom they might have formed ties, and drive them to despair, ruin, and suicide. The feds also engaged in long-term secret programs to test the effects of radiation on poor people, carrying out medical experiments that sickened and sometimes killed women, prisoners, and even children in state care.

Beginning in the 1970s and continuing through the 1990s, investigative journalism, along with declassified FBI and CIA files, revealed a series of appalling secret government programs. To pick just one: in MKUltra, the CIA and the army explored the use of mescaline and LSD by dosing unwitting civilians, including mental patients, prisoners, and johns visiting sex workers at covert CIA-run brothels. The records of that program were deliberately destroyed by the government in 1973.

But all those plots were, in the end, exposed, as were Watergate, the Iran-Contra scandal, and the NSA’s spying on Americans. Antigovernment conspiracy theorists tend to overestimate the ability of bureaucrats to scheme in secret. Grand conspiracies are hard to conceal. Yet it’s not unreasonable—at all, even a little bit—to believe that the government is still engaged in nefarious and secretive behavior, because we know that it has done so in the past. Timothy Melley, an English professor at Miami University, has written in recent years about the growth and alarming secrecy of the national security apparatus, which we glimpse through redacted FOIAs and anonymous whistleblowers, and reflect back onto ourselves in the form of TV shows like Homeland and House of Cards.

“Twenty-five years after the end of the cold war, the U.S. has 17 intelligence agencies employing hundreds of thousands of workers at a cost of some $70 billion per year,” Melley wrote in the New York Times in 2015. “But most of our ideas about U.S. intelligence work come from the endless stream of melodramatic entertainment in movies and on TV. The public thus finds itself in a strange state of half-knowledge about U.S. foreign affairs. When ‘top secrecy’ and ‘plausible deniability’ are widely accepted ideas, is it any surprise that so many people believe political power is wielded by powerful, invisible agents?”

We have found ourselves at a point in history where both real government conspiracies and their shadows loom large in our collective imagination. Those two things, working in tandem, destabilize the public perception of what’s true, what’s possible, and what we’re ready to pin on those running the country. But the problem goes beyond how civilians feel about the government; it also works, more alarmingly, in reverse. There are dozens of examples of feverish conspiracy thinking driving state action, where imaginary enemies and nonexistent plots have led to some extremely dark decisions. President Richard Nixon is our best worst example of this: he was, for one thing, a genuinely paranoid person who kept a long and well-organized enemies list and, in a double whammy of conspiracism, believed Communist-backed plots against him were orchestrated by Jews. That allowed him to justify his own conspiracies: tapping the phones at the DNC headquarters, the Watergate break-in, and bribing the burglary team themselves to stay quiet about their work.

During the Red Scare of the 1940s and 1950s, too, a fear of Communists infecting the country like termites in wood led to a shameful period of life-ruining witch hunts, hearings, and professional blacklists. (Richard Nixon, then a congressman, enthusiastically joined the House Un-American Activities Committee, which investigated suspected Communist sympathizers, to participate in the persecution.) Or, just a few years before, the incarceration of Japanese Americans in internment camps was based on nothing more than a racist suspicion that they were enemy agents organizing from within against the United States. When, beginning in the 1980s, right-wing extremists started to claim that the government planned to imprison political dissenters in camps run by FEMA, they used the Japanese internment as a reason why the theory was plausible.

More relevant to our own age is yet another phenomenon: politicians who willingly fan the flames of conspiracy either out of genuine belief or because it suits their political ends or some mixture of the two. Hillary Clinton blamed, with a straight face, a “vast right-wing conspiracy” for the women making sexual abuse claims against her husband, the president. The Bush administration infamously claimed that Iraq had weapons of mass destruction to justify its invasion of the country. Deputy Secretary of Defense Paul Wolfowitz enthusiastically promoted the idea that Saddam Hussein, not Osama Bin Laden, was the hidden hand responsible for 9/11. And beginning around 2010, with the rise of the Tea Party, we saw dozens of state and local politicians claim that Muslims were taking over their towns with the canny use of Sharia law. Many of the same politicians, including Republican senator Ted Cruz and now–Texas governor Greg Abbott, also claimed repeatedly that the United Nations had developed plots called Agenda 21 and Jade Helm, designed to invade the United States and take our guns. Whether they believed such things to be true (they weren’t), the claims served as useful focal points for organizing their supporters.

With the arrival of Trump, politicians have also—in a twist reminiscent of Nixon conspiring against the imaginary enemies he feared—taken to generating what they themselves have scornfully termed “fake news.” The Trump administration launched its own weekly news service on social media in 2017, dedicated entirely to positive coverage of the president. The same year, the Associated Press discovered that the Republican Governors Association created what looked a whole lot like a website for a news outlet: it was called The Free Telegraph and it shared positive news about—you guessed it—Republican governors, alongside negative headlines about Democrats. Until the AP started asking questions, the site did not disclose who was behind it.

Excerpted from Republic of Lies by Anna Merlan. Copyright 2019 by Anna Merlan. Published in April by Metropolitan. All rights reserved.