Yesterday, Iran claimed responsibility for launching 12 missiles at two military bases in Iraq, at least one of which housed U.S. personnel. The Pentagon confirmed these strikes, which were retaliation for last week's targeted U.S. drone strike, which killed Iranian Quds Force commander Qasem Soleimani.

According to national security adviser Robert C. O’Brien, that original attack was meant to deter “future Iranian attacks” against Americans. President Trump later warned that the United States had “targeted 52 Iranian sites” and would attack them if “Iran strikes any Americans, or American assets.”

The airstrike targeting Soleimani and Trump’s subsequent rhetoric marked a significant escalation in the tensions between the United States and Iran. Iran did not respond by backing down, as Trump hoped. Instead, it retaliated by launching missile attacks against a base or bases where US troops were stationed.

In theory, escalation can demonstrate resolve. According to deterrence theorists, by escalating a crisis the United States can show its willingness to commit resources to protect American interests, and deter adversaries from future actions

Iran’s response illustrates that such attempts are rarely successful. We still don’t know much about the logic behind Iran’s specific choice of response, or how the US might respond in turn. But even without this information, we can identify four reasons why deterrence by escalation is difficult to achieve — and why it’s especially tough in the case of the United States and Iran.

Coercion requires a clearly communicated goal

In international-relations theory, one country’s effort to get another country to do something it wouldn’t otherwise do is called “coercion.” For coercion to be successful, the adversary needs to know exactly what the coercer wants it to do and what steps it can take to avoid additional punishment.

In this case, it simply wasn’t clear what the United States was trying to coerce Iran into doing — or stop doing. Trump’s tweets suggested the airstrike was a retaliation for Iranian action against the United States.

But the United States didn’t explicitly state what Iran needed to do to avoid future U.S. action or to prompt the United States to de-escalate.

Furthermore, the attack against Soleimani seemed like a decapitation strategy — the removal of a leader to effect policy change — rather than a deterrence strategy.

Escalation strengthens the adversary’s resolve

Escalation allows the adversary to adjust expectations and increase its resolve. As political scientist Van Jackson explains, the coercer must “keep upping the ante” because the “power of punishing actions wears off over time."

For example, during the United States’ Operation Rolling Thunder in the 1960s, the North Vietnamese government pointed to the bombings’ destruction to boost anti-American sentiment and strengthen its population’s resolve to fight.

Similarly, the United States has employed an escalation strategy against Syria’s use of chemical weapons, increasing the number of missiles used in its airstrikes over time. Evidence suggests that this strategy boosted Syrian President Bashar al-Assad’s resolve to keep fighting.

What’s more, the coercer’s adversaries can benefit by escalating in return. In my recently published article in the Journal of Global Security Studies, I find that adversaries — those targeted by coercers ­­— who respond to a threat by escalating a dispute are less likely to be threatened in the future.

In other words, Iran may have had its own incentive to escalate, signaling its resolve by doing so. For sure, Iran has successfully used escalation as a strategy in the past.

We don’t yet know how the US will respond, or how Iran will respond in turn to that response. We do know that this dynamic can lead to a dangerous spiral in which both Iran and the United States escalate the conflict to demonstrate their willingness to fight. That’s what appears to be happening. Even before its retaliatory attack, Iran vowed it would retaliate and would no longer follow “any limitations in operations” from the 2015 nuclear deal. Meanwhile, the Pentagon announced it would deploy 3,500 additional troops to the region.

Escalation sends the wrong signal about U.S. resolve

For coercion to succeed, the adversary must believe that the coercer is willing to fight to protect its interests. At first glance, the airstrike would seem to demonstrate that the United States is quite determined to protect its interests in the region. But, counterintuitively, escalation can instead suggest that the coercer is not fully dedicated to a policy or course of action.

By choosing to first use an airstrike, then ratcheting up the response through Trump’s rhetoric and the deployment of additional troops based on Iran’s reaction, the United States may have signaled that it would rather not dedicate larger and more costly resources to the conflict.

As I show in my book, this can undermine the coercer’s reputation for resolve. And that, in turn, further limits the coercer’s ability to make effective threats and achieve its foreign policy goals in the future.

Trump coupled the airstrike with other signals that suggest he does not want a war with Iran. And he gave mixed messages in the past about American strategy toward Iran and the Middle East more broadly. These mixed signals further undermined the president’s ability to communicate his resolve to Iran. That’s especially true, because Trump had already acquired a reputation for using bombastic rhetoric with little clear follow-through.

My research shows that the reputations leaders acquire early during their tenures are difficult to change. It may just have been too late for Trump to alter his reputation for lacking credibility.

Airstrikes are a poor coercive tool

The airstrike further demonstrated a lack of resolve because it is less politically costly for the United States than other types of military force and puts few American lives at risk. As a result, such strikes often don’t work as a tool of coercion.

That’s even more true with a drone strike, like the one that killed Soleimani, which all but eliminates potential American casualties and is comparatively cheap and easy for the United States to employ.

Drone strikes, therefore, may have been read as a signal that the United States is not willing to dedicate resources to a cause. Sending in more troops is a stronger sign of resolve. But using the airstrike as an opening salvo may have harmed Trump’s ability to communicate his resolve in the future. What’s more, given Trump’s repeated desire to reduce U.S. involvement in the Middle East, the United States may have appeared unready to fight.

All of this leads to a highly risky strategic situation. The Trump administration appears to have believed that if it escalated the conflict, Iran was likely to fold. Iran, in turn, may believe that the Trump administration is likely to back down if it inflicts serious costs. This is a recipe for future escalation on both sides and future instability.

Danielle Lupton (@proflupton) is an assistant professor of political science at Colgate University and the author of “Reputation for Resolve: How Leaders Signal Determination in International Politics” (Cornell University Press, 2020).

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