Following his April 11 tweet that missiles “will be coming” in Syria, President Trump on Friday night announced U.S. airstrikes in multiple sites, including Damascus. The targeted sites were ones believed to be capable of storing chemical weapons and/or chemical precursors. The attacks were carried out in retaliation for last week’s alleged chemical weapons attack by President Bashar al-Assad’s regime.
This is not the first time President Trump has ordered airstrikes in Syria, of course. Last April, Trump used airstrikes against Shayrat Airbase in the aftermath of another chemical attack by the Assad regime. Even though the strike appears to have been much larger than last year’s, this remained an airstrike-only operation.
Why did Trump opt for airstrikes again to retaliate against the regime? In a recently published paper in the Journal of Global Security Studies, we examine why countries use air power.
Airstrikes are one of many tools that states use to get what they want in the international system. Given that not all policy tools are appropriate for all crises, our research examines the circumstances when states choose to use airstrikes over other options (such as economic sanctions or ground campaigns) as a coercive tool.
Reliance on air power has greatly increased in recent decades as technology and targeting have improved. Drawing on earlier work, we consider the ways that air power is used in modern warfare. Importantly, we find key differences between the choice to use airstrikes alone (as occurred in NATO’s war for Kosovo in 1999) and uses of air power in conjunction with boots on the ground — like the 1991 Gulf War.
Here’s how we did our research
We look at all international crises, based on the Interstate Crisis Behavior Project, that occurred between 1908 and 2006. We used a range of primary and secondary sources to collect new data on whether or not air power was used in each crisis, and how air power was deployed. We also looked at political goals in the crisis to see how a country’s choice of foreign policy tools relates to the stakes of the crisis.
Democracies aren’t more prone to use airstrikes — but rich states are
We looked at some popular expectations about why states would choose air power. Traditionally, there is the perception that democracies are more likely to use airstrikes — and only airstrikes — because democratic leaders are too afraid to put boots on the ground and risk casualties.
Policymakers and even potential target states themselves have shared this perception. Since the U.S. withdrawal from Vietnam, numerous militarily weaker states have gambled on their ability to outlast American public acceptance of casualties.
Contrary to popular perceptions about the cost sensitivity of democracies, we find that democratic states are not more likely than their autocratic counterparts to employ air-only campaigns. But rich states — and by extension, militarily powerful states — are more likely to use airstrikes. This dynamic helps us understand Saudi Arabia’s military campaign in Yemen, for instance.
Airstrikes are more likely when the stakes for an intervener are low
The second popular expectation we examine is whether or not airstrikes are a signal of low resolve. Do rich and powerful states just use air power when they don’t care enough to put boots on the ground? Both Saddam Hussein and Slobodan Milosevic certainly acted like they believed just that — they attempted to resist U.S.-led airstrikes on multiple occasions.
We found support for the idea that lower stakes make an airstrikes-only strategy more likely. In high-stakes conflicts, states are much more likely to couple airstrikes with ground forces. With airstrikes alone, targets may rightly infer that the crisis is a lower foreign policy priority for the attacking state. Of course, those leaders conducting the airstrikes may argue that airstrikes are a costly signal of future uses of force.
While airstrikes may indeed be used as a means of escalation, states are likely aware that airstrikes are a limited signal — and realize that the most salient crises cannot be resolved with airstrikes alone or without a stronger signal of resolve.
Airstrikes alone as a crisis response may thus lead the target to conclude that the attacker is unresolved. This may lead the state being attacked to hold out, and not make major concessions.
Airstrikes alone are not particularly effective
When states choose to use airstrikes alone, do they work?
In previous research (Understanding the impact of air power), we found that air power strategies that include efforts to deny targets military capabilities as well as punish target publics and regimes are more likely to be successful. The April 2017 airstrikes on Shayrat Airbase represented only a minimal effort at military denial, and therefore, it is unsurprising that, despite the wealth and military superiority of the United States, there was no long-lasting impact.
The bottom line
President Trump’s decision to employ strikes is not particularly surprising. Leaving aside his own personal views, he is the leader of a rich state with few good military options in Syria, a country where the stakes for the United States are relatively low.
For a second time in his presidency, Trump has chosen airstrikes. It probably won’t be the last.
Susan Hannah Allen is an associate professor at the University of Mississippi whose research focuses on coercion in the international system. Find her on Twitter @lady_professor
Carla Martinez-Machain is an associate professor at Kansas State University whose research explores military effectiveness and public perceptions of the military. Find her on Twitter @carlammm.