Boris Johnson, newly elected leader of Britain's Conservative Party, leaves a private reception in central London on Tuesday. (Toby Melville/Reuters)

As Boris Johnson gears up to lead the United Kingdom, Brexit isn’t the only crisis the new prime minister will have to navigate. Johnson also inherits spiking international tensions in the Strait of Hormuz, where Iran seized a British-flagged oil tanker, as friends and enemies alike deal with the fallout of the U.S. withdrawal from the Iran deal. Here’s a refresher on what we know about new leaders and international crises.

New leadership at home can create risks in foreign relations.

Leadership turnover can create a strategic setting in which new leaders and their foreign opponents alike have incentives to take actions that increase the risks of military conflict.

The argument has three premises. First, new leaders’ predecessors can rarely bind them to specific foreign policies. Second, as scholars who study leaders and international relations have shown, leaders differ in their willingness to resort to force, the extent to which they care about reputations, how they view the need to demonstrate resolve and their prioritization of foreign policy issues. Third, foreign states are uncertain over just how much new leaders differ from their predecessors; campaign rhetoric may have been empty and, even if it was sincere, the role of “national leader” carries with it a different set of incentives and pressures than “candidate.”

New leaders have what we call private information about their willingness to use force (i.e., their resolve) and incentives to bluff about it. It’s typically valuable for foreign states to believe a leader willing to use force — that is, for that leader to have a reputation for resolve — because those foreign states will offer better terms in crisis bargaining. But that creates an incentive for everyone to claim to be resolute, whether they are. And when diplomatic talk is cheap, the only way to prove that you’re willing to fight, and to earn the benefits of a reputation for resolve, is to fight … or to at least escalate the risks of a fight breaking out. But their opponents also have an incentive to push harder than they otherwise might, to learn just what kind of leader they’re dealing with. In my research on leaders, I call this tragic confluence of incentives “the turnover trap.”

An international crisis can be more dangerous when a new leader is in command

In a recent article, Cathy Wu and I find evidence consistent with the turnover trap’s key prediction: international crises (like the one playing out in the Strait of Hormuz) are more likely to escalate to the use of force early, rather than late, in a leader’s tenure. This is especially true for rivals, or pairs of states that view one another as long-term threats.

The good news is that the risk of escalation goes down over time, as continuing interactions reveal more information — as new leaders develop reputations that other nations can use to craft their bargaining postures. The months immediately following the accession of a new leader are the riskiest for crisis escalation — think, for example, of President John F. Kennedy and Soviet leader Nikita Khrushchev’s summit at Vienna in 1961, when the new American president had to show that he wouldn’t be “pushed around” as Khrushchev upped the ante over the status of Berlin.

What this means for Boris Johnson’s Britain

What does all this mean? Johnson did serve as foreign minister from July 2016 to July 2018, and he hails from the same party as his predecessor, which might indicate some policy continuity. But Johnson has never led his country through a serious foreign crisis, and he’s not exactly known for his predictability. How he’ll behave as the head of government — what might push him toward war and what won’t — remains largely unknown.

Springing the turnover trap in the middle of the Hormuz Crisis ensures that Johnson has incentives to look resolute, and that Iran has every incentive to escalate and see just what kind of individual lives at 10 Downing Street.

But there’s reason to temper that pessimism. Reputations are worth fighting for, and the information they provide worth learning, only if new leaders expect to stay in office. In Brexit Britain, where commentators were already talking about the possibility of a fall election before Johnson took office, cultivating or attributing reputations may not prove worth the costs and risks of escalation.

And here’s the most comforting thought for those keeping a close eye on the still-unfolding situation in the Strait of Hormuz. While leadership turnover may make crises riskier, the risk of any one crisis escalating to full-scale war is generally low.

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Scott Wolford is associate professor of government at the University of Texas at Austin. He is the author of “The Politics of the First World War: A Course in Game Theory and International Security” (Cambridge University Press, 2019). Follow him on Twitter at @thescottwolford.