Congratulations!

Thank you Shana!

Special thanks to @gdavidarceneaux.bsky.social, @sgadarian.bsky.social, @lanoszka.bsky.social, Ryan D. Griffiths, and Amy King.

In sum: during crises, allies want to see credible, costly signals, and the United States has a range of military and diplomatic toolkits. Insights from costly signaling theories apply well to alliance reassurance.

Interestingly, all three effective tools had substantively similar effects. Military signals (conventional or nuclear) and public remarks seem substitutable—in contrast to claims that actions always outweigh words. But diplomatic overtures towards adversary fail to reassure.

I examined how each U.S. policy response influences the perceived safety of South Korea from DPRK aggression—a direct measure of reassurance.
The results:
Conventional and nuclear signals work;
Public statements of support also work; but
Diplomatic overtures do NOT work.

To address this gap, I fielded a survey experiment with South Korean citizens during a hypothetical North Korea–ROK–U.S. crisis. I tested four tools: conventional signals, nuclear signals, statements of support, and diplomatic overtures to the adversary.

So what reassures allies in times of crisis? Most research examines reassurance success indirectly (e.g., allies don’t proliferate, so they are reassured). Policy tools for reassurance are many, but empirical evidence is thin.

In fact, reassurance may matter most when allies face imminent threats during crises—precisely when allies want their patron’s support most. Failure to reassure at those critical moments could have lasting impacts.

Skeptics may wonder if Washington will care about reassuring its allies (given its recent behavior). But I find it unlikely that the U.S. would sit idle if a core ally is caught in a serious crisis.

When alliances serve your strategic interests, reassuring allies is key to managing them well. So it's important to understand what tools help a patron like the U.S. actually reassure its allies.

In sum: great power shocks generate ambitious bids for independence—but these moments shape the timing of secession more than the outcomes. Hope this piece adds to growing efforts to connect international and domestic dynamics of state birth.

Using a global dataset of secessionist movements (1900–2011), we find that great power shocks strongly increase the onset of secessionist movements, but have little effect on their success. The results are robust across different measures of shocks and model specifications.

But here’s the catch: while secessionist onsets spike, their success rate doesn’t. New movements often emerge too quickly, lack capacity, and collapse once metropoles recover. In other words, sudden great power shocks create secessionist "bubbles."

Our paper shows how great power shocks—like the end of World War I, World War II, or the Cold War—produce bursts of secessionist movements across the globe. Why? Because they temporarily loosen the grip of powerful metropoles and create windows of opportunity.

Most research on secession focuses on domestic factors—ethnic divisions, economic grievances, or institutional legacies. That makes sense: secession always arises from local contexts. But it is also embedded in broader international dynamics.