Nonproliferation Professor’s New Book Examines Why Deterrence Didn’t Work in Syria—But then Compellence Did

Then in 2013, Syria formally acceded to the Chemical Weapons Convention (CWC).

“Conventional thinking suggests that compellence is harder to achieve than deterrence because it’s publicly visible that the leader has yielded to pressure or threats. In Syria, exactly the opposite happened,” said Jeff Knopf, professor and program chair of the Nonproliferation and Terrorism Studies program. “We had a nice little academic mystery.”

That exploration is now a book.

Written with two coauthors, Wyn Bowen and Matthew Moran from King’s College London, Coercing Syria on Chemical Weapons has been published by Oxford University Press.

The Assad regime’s systematic use of chemical weapons during the Syrian civil war represents one of the most significant failures of international deterrence in recent decades. Beginning in 2012, Syrian government forces repeatedly deployed sarin, chlorine, and other toxic agents against civilian populations and opposition forces, with NGOs estimating some 300 chemical attacks throughout the conflict.

“Every time we thought we were close to the finish line on this book, there’d be a new chemical attack,” said Knopf. 

We recently spoke with Knopf about the book’s findings and what lessons we can draw for the future. 

What did you find about how deterrence and compellence played out in the case of Syria?

We looked at the existing research literature and pulled out three explanatory variables. The one that gets the most attention is credibility—if your threats are credible, the other side will believe them. But there are two other factors: the balance of motivations (who cares more or has more at stake) and assurances. Thomas Schelling explains assurance as: if you warn somebody, “Take one more step or I’ll shoot,” you’re implicitly promising that if they don’t take the step, you won’t shoot them.

A lot of times, threats fail because there’s no assurance. This was famously why Saddam Hussein never told the U.S. he had no WMD—he thought Bush wanted to invade no matter what.

Our analysis was that the traditional literature has overstated credibility, and the real secret was in these other two factors. It just mattered for Assad so much more than for the U.S. For Assad, this was literally survival. For the United States, it was just enforcing a norm against using chemical weapons. Those motivations didn’t stack up—Assad was willing to go ahead no matter what.

The other problem was that Obama declared early on that U.S. policy was to remove Assad from power because he was such a brutal dictator. Therefore, Assad thought, “Even if the rebels don’t overthrow me, Obama will still try to push me out.” His motivations plus the lack of any assurance made him want to use chemical weapons.

What changed after the big gas attack in 2013: The U.S started preparing for military retaliation, and it became clear that if Syria used chemical weapons even one more time, Obama was going to retaliate. This added credibility to the threat.

This didn’t scare Assad so much as it scared the Russians. Syria was Russia’s last real ally in the Middle East. Russia had learned a bitter lesson from Libya—they’d allowed UN authorization for force, the U.S. promised it would be limited, then you got mission creep, and Gaddafi was overthrown and killed. Russian diplomats supposedly started calling Syria “Libya on the Levant.”

They were so freaked out that even though Assad was their ally, they basically said, “You have to give up your chemical weapons because otherwise we can’t protect you from the U.S. coming in militarily.”

So now if you’re Assad, signing the deal is better because you’ve got Russia fully invested in protecting you. Russia essentially promised, “We’ve got your back.” About two years after the chemical deal, Russia started sending its own military to Syria.

All the pieces that had been missing were there: the threat was more credible, the balance of motivations changed, and Russia was providing assurance. So Assad signed the chemical deal.

Unfortunately, that didn’t end the story. Syria eventually resumed using chemical weapons, initially chlorine, which isn’t banned because it has peaceful uses. Syria had also cheated on the deal, keeping back some nerve agents. Under Trump, Syria resumed sarin attacks. Trump launched airstrikes but never fully established deterrence. Syria kept using chemical weapons until Assad thought he had won the civil war. We later found out that wasn’t true—last year he got overthrown in a big surprise.

What is something you learned working on this book that has stuck with you?

If anything, I learned how difficult it can be to translate a concept into reality. Everybody treats credibility like it’s really straightforward—a binary concept where either the threat’s credible or it’s not, and everybody can see it. But often it was very hard to tell.

For example, in 2017, after a sarin attack killed about 100 people, Trump responded by launching 60 cruise missiles at the Syrian air base from which the attacking planes had taken off. The commentary afterward ranged from people celebrating—”Trump makes American credibility great again, he finally took military action when Obama wouldn’t”—to others saying “Trump wimped out, it was a pathetic pinprick attack that can’t possibly restore deterrence.”

In real time, people were looking at the same action and coming to utterly opposite conclusions about whether it creates credibility. Our response isn’t that one person’s right and one’s wrong—it’s that inherently it’s often ambiguous. Where’s the threshold? How much do you have to do before people actually think your threats are serious? These concepts that policymakers work with as if they’re cut and dried can have a lot more ambiguity in practice.

In 2025, why is it worthwhile to look back at what happened in Syria a decade ago?

Some things about the Syria case were unique—very few governments will gas their own people. But we know there are still actors around the world that possess various WMDs, so there will probably be future cases where the United States or other actors will want to try to deter somebody from using chemical weapons.

We hope there’ll be policy lessons from the book. One is how to assess your odds—do you have a good chance of being successful with deterrence, or is it really unlikely to work? If it’s not likely to work, you might want to go back to the drawing board and consider other policy options. If you think you can do it, then what’s the whole range of factors you want to take into account to craft the most effective deterrent posture possible?

One place where both Obama and Trump fell short is they never really thought through what it would take to deter Assad. We coined a phrase—we call it the “resolve plus bombs formula.” They said, well, if you talk tough and threaten to launch some cruise missiles or drop a few bombs, you’ve fulfilled the formula for making deterrence work. It was pretty clear that was never gonna work with Assad. It wasn’t a big enough threat relative to what was at stake for him.

This is almost unconscious—it’s just the way deterrence is always practiced in the United States. Getting policymakers to be more mindful about what they actually have to take into account in a specific situation, what they actually have to do to craft a deterrent threat that could be effective—I’m hoping that’s a finding in the book that will still have legs going into the future.

What’s been most personally rewarding for you?

I was really happy about where the book got published. It’s being published by Oxford University Press in a special series called “Bridging the Gap.” The idea is to bridge the gap between ivory tower theoretical work on international security and real-world policy concerns—the book will have findings that could be useful to the policy community, not solely contributing to scholarly academic literature.

The name of the series comes from work done by Alexander George, who coined the term “coercive diplomacy.” Alex was my dissertation advisor when I did my PhD back in the day, so just to me personally, it was really meaningful to get published in this series that was named in honor of my mentor and dissertation advisor.