Eight days after Donald Trump was elected president, Yale history professor Timothy Snyder posted an ominous warning on Facebook.

Americans are no wiser than the Europeans who saw democracy yield to fascism, Nazism, or communism,” he began. “Our one advantage is that we might learn from their experience. Now is a good time to do so. Here are twenty lessons from the twentieth century, adapted to the circumstances of today.”

Within days the post had gone viral, accumulating over 17,000 shares on Facebook and making headlines across dozens of websites. The “20 Lessons from the 20th Century,” as the post came to be called, focused a national spotlight on its author.

Even before his post, Snyder had been no stranger to fame. A distinguished historian of Eastern Europe, particularly of the rise of totalitarianism and the Holocaust, Snyder has long attracted adoration and criticism for his work. He has gathered numerous accolades, including an Andrew Carnegie Fellowship and Havel Foundation prize, and written several award-winning and bestselling books. Still, Snyder was surprised by the popular reaction to his post, from online hits to random hugs in New York City.

“I did not think when I wrote it that, within a few days, it would be the thing that I was best known for,” Snyder said in an interview with The Politic.

“It’s not a historical thing,” said Snyder. “But I couldn’t have done it without the 25 years of work [I spent] trying to understand history.”

***

In the 1980s, when Snyder was studying history and political science at Brown University, communism collapsed in Europe. That shifting political context pushed Snyder to think about intellectual and diplomatic history, two areas of study that would later define his professional career. After graduation, Snyder received a British Marshall Scholarship for history graduate work at Oxford. And yet, despite his extensive studies in the field, Snyder did not intend to become a historian. After all, his favorite subject in middle and high school was math. In college, he hoped instead that history would lay the foundation for a career in journalism or diplomacy. It wasn’t until Snyder wrote his dissertation at Oxford that he decided to become a full-fledged historian.

By the time he arrived at Yale in 2001, Snyder already had a distinguished career. After receiving his doctorate from Oxford, Snyder served as an Academy Scholar at Harvard’s Center for International Affairs until his move to Yale. In 2012, Yale appointed him Bird White Housum Professor of History.

As a historian of a region underrepresented in Yale’s academic landscape, Snyder felt obligated to ensure that his students could learn from it. From that sense of responsibility emerged the two-part lecture course for which Snyder is best known at Yale: Eastern Europe to 1914 and Eastern Europe since 1914. The scope of the history covered in these two courses, beginning in the 800s and ending in the modern day, far exceeds Snyder’s narrow academic focus on the rise of totalitarianism in twentieth century Eastern Europe.

Snyder had a monumental challenge before him: understanding the entirety of Eastern European history well enough to teach it.

“[It’s] pretty much the hardest thing intellectually I’ve ever done,” said Snyder, of crafting and teaching the class. “I try to make it look easy, but actually getting all the countries, all the empires, the themes [and] putting them into an order, follow a logic where the students can go from whatever they’ve got to confident knowledge, that’s really hard.”

Snyder credits the process of designing the course with making him a better historian — it forced him to read more of the historical literature and fill the gaps in his knowledge. He has been glad to see so many Yale students eager to learn about a region they previously knew nothing about. But ultimately Snyder’s most satisfying experience as a professor was witnessing the course become something that “felt like a class to the students just as it felt like a class to [him].”

Yale students, for their part, love Snyder’s lectures. His courses have become some of the history department’s most popular, with consistently positive evaluations and rising enrollment. Students usually cite Snyder’s engaging style and commanding presence to explain his success as a teacher. Zeshan Gondal ’19 appreciated Snyder’s use of humor and fearless tendency to “make self-deprecating jokes.” Another student, Wesley Kocurek ’19, found Snyder’s willingness to “inject his personality into the course” refreshing.

“He kind of dumps information on you in the lectures, but it’s fun [and] informative, and he obviously knows his stuff,” Kocurek said. “You just get the sense that he’s an extremely intelligent man who needs to speak quickly because that’s how fast his thoughts are moving. It’s almost like he’s frustrated that we’re not in his head.”

Much of Snyder’s work aims to get people to see what’s in his head. Snyder believes an essential part of history is communicating a certain idea to people who don’t already have it. Historical scholarship, in his view, exists to help people “understand a moment.”

“I think [history] is both the science of trying to understand and the art of trying to convey,” Snyder said.

Snyder describes the first part of his approach to history as a chase to “trap the truth.” His view of history as a series of moments suggests the historian’s task is an impossible one, because each moment always gives way to the next. But through extensive research, historians can trap a moment. Once they have locked a moment into a place from which “it can’t get out,” they move on to what Snyder calls the “literary part”: helping people understand what the historian already does.

This literary view has influenced how Snyder tells stories in his lectures and books to teach history. Many students have praised his storytelling style, which presents history not as a collection of facts but as a rich and complex chronicle. Through his storytelling, Snyder helps his students understand the past and how it clarifies the present.

“The present is like a river and the past are like stones that you can stand on,” Snyder said. “It’s good to have more stones, because everything is in flux all the time. You need ways to stand still and look around, and the past can help with that. I think this is a time when history does have something useful to say about the present, and I’m trying to do that.”

For years, much of Snyder’s focus was directed abroad. He had dedicated himself to drawing connections between Eastern Europe’s past and its present. In 2015 he published Black Earth: The Holocaust as History and Warning and wrote articles warning against Vladimir Putin’s rise. Then came Trump.

***

“Psychologically it was the first thing that I could do,” Snyder said of his post after Trump’s victory. “When things happen that you process as being devastating, the strongest temptation is to do nothing.”

But in the days that followed the election, “I felt this weight on my chest that I had to get off. I write. So writing something was the first thing I could think to do,” he said.

When Snyder drafted his now-famous “Twenty Lessons,” he consulted his wife, fellow Yale professor Marci Shore. Shore also teaches Eastern European history but covers it through intellectual and cultural trends.

The two met in 2002, while Shore was still a postdoctoral fellow at Columbia’s Harriman Institute. Snyder was interested in writing about the Polish-Jewish Berman family in Warsaw, which she had researched in both Poland and Israel. In 2005, the two married in Cracow, Poland. While they don’t collaborate on any projects, they do read each other’s work.

Usually Tim is impatient and wants to publish quickly, and I tend more often to be in favor of waiting, rereading, editing, contemplating the best venue,” said Shore. “But in this case the urgency of the moment was such that I was, uncharacteristically, in favor of posting immediately.”

Snyder agrees that he is impatient. By his own admission, everything seems to be moving very slowly, and he wishes “it would go more quickly.”

Snyder feels that though the “world” may have felt he was rushing ahead – he published his post on November 15, only a week after Trump’s election victory – from his perspective, he was behind. He wrote the twenty points quickly, and didn’t wait long before submitting them to The New York Times, which turned his piece down. After consulting with Shore, he decided to publish in a public Facebook post, which he now sees as a “smart” move, since that allowed any news outlet to share it. The Dallas Morning News was the first, followed by In These Times, and then a flurry of sites ranging from The Huffington Post to the History News Network.

Not everyone has appreciated the speed with which Snyder has warned his listeners about the Trump presidency. Many accused Snyder of exaggerating Trump’s threat and sounding the alarm bell too soon. But to Snyder, such criticism falls flat. He acknowledges that he may be wrong – he says he would be “delighted” if he were – but insists the stakes are too high to stay silent.

“If your choices in life are alarmism and authoritarianism, which one would you choose?” Snyder said. “If those are really the risks, then take your pick. Is [it] such a big deal to be made fun of a little? The other possibility is that your children and your grandchildren will grow up in a country that is not free.”

Snyder dismisses alarmism charges because he feels they come from those who would prefer “to do nothing.” Such claims, he argues, enable a dangerous complacency. One can insist that nothing about the world has changed, but such a fixation usually leads one to miss the subtle changes until it is too late.

“At any moment, any given second, [nothing is wrong],” said Snyder. “And then the next second is a little worse, the next second is a little worse, [but] you can always at each point say ‘Don’t be alarmist,’ because not much has changed today or this hour. It’s always easier to sit back and say ‘This is normal,’ then maybe get popcorn and watch Clint Eastwood movies. Anybody can do that.”

To Snyder, the real difficulty lies in spurring action. In order to motivate people to act and not simply sit back, Snyder is willing to be mocked, and he is willing to be wrong. And as far as he is concerned, his warnings up until this point have been relatively moderate, even if many people don’t see it that way.

“I’m more radical than most people,” said Snyder. “But I’m less radical than everyday life.”

***

Snyder’s focus on authoritarian threats to democracy crystallized during his trips to Eastern Europe throughout the 1990s. Those travels proved crucial for his intellectual development because these places – from Poland to Belarus to Ukraine – became “more real” to him.

“You can’t write about places unless you feel intellectually and emotionally comfortable with [them],” he said.

Snyder’s work focuses on places rather than on historical figures or ideological currents. Instead of writing about a nation, he observes how different nations and crimes have converged on a single place. The darkness of the places that Snyder ultimately chooses led a reviewer of one of his books to call him a “historian of evil.”

And as a person who has spent his career studying the cruelest crimes humanity has ever perpetrated, Snyder has more than earned the label. His most famous book, Bloodlands, recounts the scale of human suffering inflicted on the lands between Nazi Germany and Soviet Russia with arresting details of mass starvation, familial cannibalism, and wholesale slaughter. Black Earth explores Ukraine as the site of the Holocaust’s worst atrocities. Snyder acknowledges the challenges of writing about the annihilation of millions of lives, especially when the scale of the tragedy can obscure its human element.

What I’m trying to do is get the reader to identify with people as individuals,” says Snyder. “Even if I can’t come close to doing the life justice, if I’ve made the person who died seem real, then that death is somehow registered in the reader, and then the reader can think about the numbers differently. A tragedy in which twelve people die is different from a tragedy in which 12,000 people die, but I don’t think we can understand the 12,000 if we don’t understand the twelve. And I don’t think we can understand twelve unless we understand one.”

Writing Bloodlands and Black Earth was not easy. But Snyder is ultimately pleased that he took care “not to dodge.” He felt the subjects explored in his books were important ones, and that they were especially relevant to events unfolding today.

“I am glad that I took these things on,” Snyder said. “Not because it’s been pleasurable, but because I thought that those were the right things to be doing at the time.”

To Shore, that clear moral compass represents one of Snyder’s best qualities. She credits much of it to his mother, whom she describes as possessing an “unusually confident sense of moral clarity.” According to Shore, Snyder’s mother takes moral duty seriously, always considering the consequences of taking any moral maxim to its logical conclusion. Shore believes she and Snyder have internalized that emphasis on moral duty, especially as it pertains to their family.

“I think for both of us our children have added an additional moral weight to all our decisions,” said Shore. “We’re always thinking about them—and thinking about the question: what kind of world are we creating for our children?”

It is likely that sense of moral obligation that fueled Snyder’s vocal denunciations of Trump and the Facebook post that has caught the attention of thousands. Through his writings, Snyder hopes to provide actionable guidelines for an American populace unfamiliar with the threat of totalitarianism that Trump represents.

“You can’t just act,” said Snyder. “You need to have some sense of why you’re acting. I’m trying to help the American republic get some standpoints from which it can understand its own realities.”

Despite some of the criticism that he has received, Snyder is for the most part heartened by the reaction to his Facebook post. To him, it is evidence that Americans are looking for ways to take action, thus avoiding the complacency of which he is so critical. Meanwhile, Snyder is still not finished with the Facebook post. He has since expanded upon each of the twenty lessons, supplying them with historical examples and analysis, and compiled his additions into a single book named On Tyranny, to be published on February 28.

“I’m gratified,” said Snyder, of the excitement that has surrounded his twenty lessons. Then, he added with a smile, “And I’ll take all the random hugs in New York too.”