Suspicious packages containing suspected pipe bombs have been discovered across the country, targeting several critics of President Donald Trump. But historians and security experts say the packages aren’t necessarily a sign that the country is getting more violent — and that our current climate is not as violent as other periods in American history.
The FBI, along with local law enforcement, has launched an investigation into the attempted attacks on Trump critics. As of Wednesday, 10 similar packages were received at locations in New York, Washington, D.C., Florida and Delaware. The intended recipients include Hillary Clinton, former President Barack Obama, former Vice President Joe Biden, Congresswoman Maxine Waters, Democratic donor George Soros, the actor Robert De Niro, former CIA director John Brennan and former Attorney General Eric Holder, according to the FBI. So far, no motive or suspects behind the suspicious packages have emerged.
While the bombs have raised alarms, historians and experts note that America has seen several bombing attacks in the last century. Within American history, experts say, the attempted attacks are more in line with “ebbs and flows” of violence — and not a sign that the country is necessarily getting more violent. Brian Nussbaum, a professor at the University of Albany who studies terrorism and cybersecurity, says waves of widespread violence come in “ideological bursts.”
Compared to the 1960s and 1970s, the U.S. has gotten significantly less violent, most likely because several organized groups that perpetuated attacks during that era have since disbanded, says Joseph Young, a professor of law and criminology at American University. While the U.S. saw 2,500 bombings in an 18-month period between 1971 and 1972, the number has decreased by the hundreds in the decades since. According to a report from the U.S. Bomb Data Center, there were 335 bombings in 2017, a 24% decrease from the prior year.
Young points out that modern attacks, whether they are school shootings or racially-motivated violence, come from one or two actors working as individuals.
“It’s not like Weathermen Underground. They had an organized strategy,” he tells TIME. “Even the groups that are mobilizing more so than just being one or two people don’t really have the power to have effective campaigns.”
From the late 1960s to the late 1970s, Nussbaum says, radical left wing groups mobilized as part of a global wave of revolutionary violence. Organizations like the far-left West German Red Army Faction and the Italian Red Brigades inspired similar movements in the U.S., according to Nussbaum. Although the violence within that time period was frequent, the attacks were typically not intended to kill people, Nussbaum says: “It was designed to create attention. Often the bombings were called in ahead of time and occurred in the evenings, when buildings were closed.”
Writer Bryan Burroughs highlighted in a 2016 piece for TIME how in our current era, detonations of bombs invite interest from media, the public and law enforcement. But at one point not too long ago, bombings were so common that most Americans saw them as a routine inconvenience.
Burroughs wrote that in the 1970s, protest bombings from radical underground organizations numbered in the hundreds. Revolutionary groups like Weather Underground, the New World Liberation Front and the Symbionese Liberation Army frequently carried out attacks in cities like New York, Chicago and San Francisco. Such groups have faded in the collective memory, Burroughs wrote:
The underground groups of the 1970s were a kind of grungy, bell-bottomed coda to the protests of the 1960s; their members were mostly onetime student leftists who refused to give up the utopian dreams of 1968. While little remembered today, there was a time during the early 1970s when the U.S. government—the Nixon Administration—considered these groups a genuine threat to national security. Alarmed by a series of Weatherman attacks, Nixon told J. Edgar Hoover during a June 1970 Oval Office meeting that “revolutionary terror” represented the single greatest threat to American society. Hoover promised to do what he could, which wasn’t much.
Burroughs wrote that, starting around 1969, bombing attacks grew “by the day,” although they caused few injuries or deaths. The deadliest attack came in 1975, when a bombing of a Wall Street restaurant killed four people.
The first actual bombing campaign, the work of a group of New York City radicals led by a militant named Sam Melville, featured attacks on a dozen buildings around Manhattan between August and November 1969, when Melville and most of his pals were arrested.
Weather’s attacks began three months later, and by 1971 protest bombings had spread across the country. In a single eighteen-month period during 1971 and 1972 the FBI counted an amazing 2,500 bombings on American soil, almost five a day. Because they were typically detonated late at night, few caused serious injury, leading to a kind of grudging public acceptance. The deadliest underground attack of the decade, in fact, killed all of four people, in the January 1975 bombing of a Wall Street restaurant. News accounts rarely carried any expression or indication of public outrage.
As the bombings from left-wing groups ebbed, far right groups began carrying out attacks throughout the 1980s and 1990s, Nussbaum says. He cites attacks by the white supremacist group The Order, which funded other white supremacists through bank robberies. The surge of attacks stopped in 1995 with the Oklahoma City bombing by Timothy McVeigh, who was seeking retaliation against the government for the Waco siege in 1993. According to Nussbaum, the violence in the 1990s stemmed from a general right-wing antipathy to globalism. Conspiracy theories about a “new world order” spread as people became convinced there would be a “global government.”
“The general takeaway is that in the short term, people who want to engage in ideological violence are often able to find compelling reasons to justify their behavior,” Nussbaum says. “But that is often part of a broader political milieu that’s going on.”
Correction, Oct. 26:
The original version of this story misstated the start of a decade of violence in the U.S. that Nussbaum attributes to left-wing radical groups. It began in the 1960s, not the 1950s.
More Must-Reads from TIME
- How the Electoral College Actually Works
- Your Vote Is Safe
- Mel Robbins Will Make You Do It
- Why Vinegar Is So Good for You
- The Surprising Health Benefits of Pain
- You Don’t Have to Dread the End of Daylight Saving
- The 20 Best Halloween TV Episodes of All Time
- Meet TIME's Newest Class of Next Generation Leaders
Write to Mahita Gajanan at mahita.gajanan@time.com