Military Strikes on Syria: Historical Lessons and Implications

In the early morning hours of April 7, the United States launched fifty-nine Tomahawk cruise missiles from two destroyers in the Eastern Mediterranean against al-Shayrat Air Base south of Homs. The base was reportedly used by Syrian military aircraft that dropped chemical munitions on the town of Khan Sheikhoun earlier this week and then attacked a hospital treating the wounded, killing up to a hundred civilians, including dozens of children.

According to a Pentagon statement, the strike targeted aircraft, hardened aircraft shelters, petroleum and logistical storage sites, ammunition supply bunkers, air defense systems, and radars, while avoiding chemical weapon storage facilities. The impact on Syrian air operations is likely to be modest, as Shayrat is not one of the Assad regime's main operating bases. The primary impact is likely to be political, raising questions about whether the regime will now cease CW attacks, and whether other actors will press it to do so.

The strike was probably intended to deter further CW strikes and thereby restore American credibility. Washington's failure to uphold its 2012 "redline" regarding Syrian CW use undermined relations with allies and emboldened adversaries around the world. The regime's use of sarin gas this week, in violation of its obligations under the Chemical Weapons Convention, was thus an early test of the Trump administration. Failure to act would have further damaged American credibility, with adverse consequences in the Middle East and elsewhere.

LESSONS FROM THE PAST

How will Syria respond to the strike? Some useful insights can be gleaned from the manner in which Damascus has responded to previous military strikes, and from past U.S. attempts at coercive diplomacy.

Israeli strikes in Syria. Israel conducted a number of attacks in Syria during the first decade of Bashar al-Assad's presidency, including an October 2003 airstrike on a terrorist training camp, a September 2007 airstrike on a covert nuclear reactor, and the August 2008 assassination of Brig. Gen. Muhammad Suleiman, a senior Syrian military officer reportedly involved in the transfer of arms to Hezbollah. In each of these instances, Syria eschewed retaliation.

Since 2013, Israel has conducted dozens of airstrikes against Syrian arms convoys carrying "game changing" weapons destined for Hezbollah, including advanced Russian surface-to-air, surface-to-surface, and antiship missiles. Until recently, Damascus neither acknowledged nor responded to these strikes. Since the fall of Aleppo last December, however, Assad has twice launched surface-to-air missiles at Israeli aircraft attacking these convoys, evidently flush with confidence from his recent military victories over rebel forces. Moreover, because the Israeli attacks have focused on interdicting these shipments rather than striking sensitive regime targets, the convoys have continued over the years, with some of the weapons reportedly getting through.

Prior CW use. In August 2012, growing concerns over possible regime CW attacks against rebels and civilians spurred President Obama to warn Damascus that any use or diversion of CW was "a red line" that would "change [his] calculus." In later statements, he added that CW use would be "totally unacceptable" and would have "conse­quences," but without specifying what these were.

Ignoring these warnings, the regime incrementally escalated its use of CW over the next year, culminating in an August 2013 sarin strike in a Damascus suburb that reportedly killed more than 1,500 civilians. This attack occurred while UN inspectors were just a few kilometers away on a visit to investigate prior claims of CW use. In the crisis that followed, Syria agreed -- amid U.S. military threats -- to give up its CW capabilities and accede to the Chemical Weapons Convention. Yet it subsequently used chlorine gas against civilians and rebels, as well as sarin, indicating that it retained perhaps the most lethal element of its proscribed CW stockpile. In short, through incrementalism, obstruction, and denial, Assad was able to challenge and at times circumvent the redlines and constraints imposed on his use of CW.

These experiences show the following:

1. When confronting a determined adversary, Assad has often backed down.
2. When confronting an adversary of uncertain commitment and resolve, he has tested limits, eroding or circumventing them when possible and backing down when necessary.
3. When confronting an adversary determined to disrupt his actions without imposing major costs, he will drive on.

That said, situational factors that may have affected some of these past outcomes may not pertain today. For instance, Assad may now believe that he is on the verge of breaking the back of the six-year uprising thanks to the support of Russia, Iran, and Hezbollah, which could increase his tolerance for risk. Indeed, Syria's efforts to challenge recent Israeli strikes indicate that this might be the case. The regime also reportedly launched further strikes from al-Shayrat Air Base only hours after the U.S. strike, using aircraft carrying conventional munitions.

Coercive diplomacy in Iraq. During the 1990s, the United States used airstrikes, cruise missile attacks, and troop deployments to disarm and contain Iraq and deter its aggression against Kuwait and the Kurds. Yet Baghdad never ceased resisting the weapons inspections and no-fly zones, which it saw as infringements of its sovereignty. It sought to wear down U.S. resolve through constant acts of defiance. The United States tended to respond predictably, with limited strikes against assets linked to provocations (e.g., air defense sites that threatened coalition aircraft). This allowed Saddam Hussein to manage risk, limit the cost of brinkmanship, and thereby sustain his policy of defiance, eventually causing Washington to abandon its support for weapons inspections. Even so, it is not clear that a more aggressive U.S. approach would have been more effective; Saddam had massive quantities of military hardware to throw away and was highly motivated to resist because he believed he was fighting for his life and could not afford to appear weak.

This experience holds several key lessons that are applicable to Syria:

1. Deter­rence and coercion of determined adversaries can be challenging due to asymmetries in interests, motivation, and risk tolerance.
2. Coercive diplomacy is often difficult to sustain over time.
3. The cumulative costs of coercive diplomacy may eventually erode domestic and international support for the policy.

To be sure, the current situation in Syria is in many ways unique because Assad is so greatly dependent on Russia, Iran, and Hezbollah for his survival. As a result, his response to the al-Shayrat strike and any future U.S. actions will no doubt be heavily influenced by Russia and Iran. And all three allies will be influenced by what they hear from Washington, as well as their assessment of U.S. intentions and resolve. Thus it is unclear whether Tehran and Moscow will take the same approach; for instance, will they  encourage Assad to act with restraint, guile, patience, or defiance?

WHAT NEXT?

Experience indicates that Assad will likely continue defying the international community and challenging the CW redline, and that additional strikes may be necessary to deter him from doing so. Going forward, U.S. military actions should be guided by the following considerations, drawn from lessons learned in past efforts at deterrence and coercive diplomacy in the Middle East:

1. Do not set redlines unless the United States is willing to enforce them.
2. Answer attempts to test U.S. limits, as failure to respond will only invite additional challenges.
3. Deter further CW use and other violations through denial and punishment, both to introduce uncertainty into the Assad regime's cost-benefit calculus about future U.S. responses and to impose costs.
4. Because disproportionate responses are prohibited by the Law of Armed Conflict, respond to challenges asymmetrically; that is, don't just hit the source of the provocation, hit targets that the regime truly values. Striking "disposable" assets will only enable Assad to sustain his defiance, calibrate risk, and more safely test U.S. limits.
5. Make clear that the al-Shayrat strike is not necessarily a one-off operation. Otherwise, Assad might come to believe that he can outlast Washington once U.S. domestic opinion turns against intervention, or once the administration becomes distracted by a more pressing crisis elsewhere.

Moreover, the United States should use the threat of additional strikes to test the potential for multilateral diplomacy, pressing Syria to eliminate its undeclared CW stockpiles and honor its ceasefires with various rebel forces around the country. This is America's best hope for avoiding a "commitment trap" (whereby follow-on strikes become necessary to subdue, even if temporarily, a recalcitrant adversary), as well as the ever-present risk of mission creep and escalation.

Finally, now that it has taken direct military action against Assad, the United States should keep in mind that its best hope for an exit strategy that advances its interests in Syria (including the fight against the Islamic State and other Salafi-jihadist groups) is by fostering the creation of effective non-Salafist rebel forces that can draw Sunnis away from the extremists and apply sustained military pressure on the Assad regime. Only this will ensure that ceasefires are honored and major new refugee flows are averted. And only a military balance that produces a costly stalemate for the regime will generate the pressures needed to achieve a diplomatic solution to the war, which has been the major driver of jihadist radicalization and mobilization this decade. It may be too late for such an effort to succeed, but that should not stop the United States from trying. The alternative may be the continued production of jihadists, and an open-ended U.S. military commitment in Syria that the public may not support indefinitely.

Michael Eisenstadt is the Kahn Fellow and director of the Military and Security Studies Program at The Washington Institute.