The United States will soon reach a crossroads in its struggle against terrorism. The international coalition fighting the Islamic State (also known as ISIS) has driven the group out of much of the territory it once held and, sooner or later, will militarily defeat it by destroying its core in Iraq and Syria. But military victory over ISIS will not end the global war on terrorism that the United States has waged since 9/11. Some of ISIS’ provinces may outlive its core. Remnants of the caliphate may morph into an insurgency. Al Qaeda and its affiliates will still pose a threat. Moreover, the conditions that breed jihadist organizations will likely persist across the greater Middle East. So the United States must decide what strategy to pursue in the next stage of the war on terrorism.

On the campaign trail, Donald Trump called for sweeping changes in U.S. counterterrorism strategy, promising to “defeat the ideology of radical Islamic terrorism.” As president, he faces a broad range of choices. At one extreme, Washington could abandon its military commitments in the greater Middle East on the assumption that it is U.S. interference that provokes terrorism in the first place. At the other, it could adopt a heavy-footprint surge strategy that would involve using overwhelming military force to destroy globally capable terrorist organizations and attempt to politically transform the societies that produce them. In between lie two options: one, a light-footprint approach akin to that taken by the Obama administration before ISIS’ rise; the other, a more robust approach closer to Washington’s response to ISIS since late 2014. 

None of these four strategies is ideal. The extreme options—disengagement and surge—promise to dramatically reduce the threat. But both would likely fail in costly ways, and both are politically untenable today. The middle choices pose less risk and are more politically palatable. But they also promise far less and would likely leave the United States stuck in a protracted conflict. 

Trump must therefore pick the best of a bad lot. Despite his campaign rhetoric, the least worst choice would be an approach close to the medium-footprint strategy being used to defeat ISIS today: an aggressive campaign encompassing air strikes, drone attacks, special operations raids, and small deployments of regular ground troops in response to specific threats, all in support of efforts by regional U.S. partners. This approach is imperfect, and it will not achieve decisive victory in a conflict that shows few signs of ending soon. But it is the most likely way of delivering an acceptable degree of security at an acceptable price. 


Since 9/11, the U.S. government has proved remarkably proficient at killing terrorists, frustrating their plans, and degrading their organizations. Yet no sooner has Washington finished off one group than a more dangerous one emerges. The United States gravely wounded al Qaeda in Afghanistan in 2001–2 and the decade thereafter, only to be confronted by the rise of al Qaeda in Iraq, al Qaeda in the Arabian Peninsula (AQAP), and other potent affiliates of the group. The struggle against those organizations was superseded in turn when ISIS—the most virulent jihadist group yet—emerged on the scene. Even as the United States has repeatedly achieved operational successes, enduring victory in the war on terrorism has remained elusive. 

Even as the United States has repeatedly achieved operational successes, enduring victory has remained elusive.

This problem again looms large. As of late 2016, ISIS had lost control of key strongholds, such as Fallujah and Ramadi in Iraq and Manbij and Jarabulus in Syria. Iraqi forces, supported by an international coalition, were fighting to retake Mosul, and U.S.-backed militia groups in Syria had begun operations to capture ISIS’ capital, Raqqa. The U.S. Department of Defense has estimated that since August 2014, the coalition has killed over 45,000 ISIS fighters, and that ISIS’ combat proficiency, organizational cohesion, and morale have fallen sharply. ISIS’ defeat is now only a matter of time.

But the group’s defeat will not end the war on terrorism. ISIS’ provinces in countries such as Afghanistan, Bangladesh, Egypt, and Libya may survive. ISIS fighters in Iraq and Syria may return to their insurgent roots. Al Shabab in Somalia, AQAP in Yemen, and Jabhat al-Nusra in Syria are not going away either. Moreover, because much of the Middle East remains a fount of extremism, a successor to ISIS may arise in Iraq, Syria, or somewhere else. The United States will need a strategy for the next stage of its war on terrorism.

A peshmerga fighter above the ISIS-controlled Baretle village near Mosul, Iraq, September 2014.
A peshmerga fighter above the ISIS-controlled Baretle village near Mosul, Iraq, September 2014.


At one extreme, the United States could exploit the opportunity provided by ISIS’ defeat to adopt a strategy favored by dovish critics: military disengagement from the greater Middle East. This option would represent a radical break from recent practice and a return to U.S. counterterrorism strategy of the 1990s and even before. That would mean dramatically reducing U.S. military presence in the greater Middle East, with no combat troops remaining beyond those needed to secure U.S. embassies. Washington might still conduct a small number of counterterrorism strikes, but these would be mostly retaliatory in nature, such as the strikes on al Qaeda bases ordered by U.S. President Bill Clinton in 1998 after the group bombed the U.S. embassies in Kenya and Tanzania. Any preemptive attacks would be against only imminent threats, and only with drones or other long-distance, limited-liability methods of attack. Additionally, the United States would make no attempt to create counterterrorism partners from scratch, as it did in Afghanistan and Iraq, and would significantly reduce its existing military cooperation on counterterrorism with countries such as Egypt and Saudi Arabia. 

Disengagement would thus mean confronting terrorism primarily through nonmilitary means. At home, the United States would focus on intelligence and law enforcement. Abroad, it would focus on sharing intelligence with other countries and securing diplomatic cooperation on counterterrorism. Disengagement might involve some limited development assistance to Middle Eastern countries, but U.S. policy would not aim to fundamentally remake them. Put simply, dis-engagement would take the United States off the war footing of the past 15 years.

The logic of disengagement is simple: U.S. military involvement in the Muslim world cannot fix the problem of terrorism; in fact, it exacerbates it by sowing anger at U.S. meddling. Pulling back could therefore minimize the terrorist threat. At the least, disengagement would remove a tempting target—the U.S. military—from the terrorists’ backyard and reduce the blowback that occurs when U.S. forces accidentally kill innocent people or act in other heavy-handed ways. It would also deprive extremists of crucial propaganda material: U.S. “occupation” of the Holy Land. More optimistically, it might redirect the anger of militant Islamists away from the United States and toward their own repressive governments and prevent more moderates from radicalizing. Whatever terrorist threat remained, the argument runs, could best be handled by learning to live with occasional small attacks rather than by overreacting to them. Disengagement would mean, its proponents claim, that the United States would save billions of dollars annually by conducting fewer operations and marginally reducing the size of its military. 

ISIS’ defeat will not end the war on terrorism.

Yet disengagement would also carry severe liabilities. It would grant extremists a powerful propaganda point: that the United States will flee, not fight, when bloodied. Given Washington’s traditional role as the regional stabilizer, disengagement could also create a power vacuum in the Middle East, perhaps threatening states crucial to U.S. interests, such as Saudi Arabia.

Worst of all, disengagement would probably not actually reduce the terrorist threat. Although U.S. interventionism is one source of jihadist fury, there are others, including the United States’ liberal values and its nonmilitary support for repressive regimes, such as those in Egypt and Saudi Arabia. And although inaction might mitigate anti-U.S. blowback, it would also prevent the United States from disrupting incipient dangers—as happened before 9/11, when U.S. officials failed to deal with the growing threat posed by al Qaeda. Disengagement, then, might not take the United States out of the terrorists’ bull’s-eye, but it would deprive it of the tools needed to keep the threat at bay. And if a less aggressive posture contributed to a mass-casualty attack, leaders who had gambled on disengagement would likely face political ruin.

Given these downsides, no U.S. president is likely to embrace disengagement. It is telling that the Obama administration, despite showing some sympathy for the logic of disengagement following Osama bin Laden’s death in 2011, ultimately concluded that the strategy was neither practical nor politically viable.

People flee Mosul, December 31 2016.
People flee Mosul, December 31 2016.
Khalid Al Mousily / Reuters


A post-ISIS strategy need not take U.S. counterterrorism all the way back to the 1990s. A second, light-footprint option would wind the clock back only to the period from 2011 to 2014, after bin Laden’s death but before ISIS emerged as a major force. The logic behind this strategy holds that the United States can reduce terrorism to a tolerable level by using limited military force to fight terrorist groups capable of major attacks. But it must not go too far, because outsiders cannot fix the deep-seated political problems within the Muslim world that cause terrorism. So the United States must avoid committing too many troops or resources; the risk of getting stuck in a quagmire is as great as the risk of terrorism itself. 

In practice, this strategy would entail sustained, preemptive military efforts to weaken the most dangerous terrorist organizations, wherever they may be. Yet the United States would avoid even modest deployments of U.S. ground forces by limiting itself to drone strikes, aerial attacks, and occasional raids by special operations forces. Where ground troops were needed to contain the most lethal terrorist organizations—AQAP, for instance, or al Shabab—Washington would rely on regional governments to provide them, assisting with long-distance strikes and logistical support. In all cases, regional partners would do the lion’s share of the work. The light-footprint strategy would thus aim to manage, rather than defeat, what is considered a real but limited threat, and do so as cheaply as possible.

This approach would have its virtues. It would use the United States’ unique military capabilities, such as the ability to conduct long-range strikes, to keep pressure on terrorist organizations without creating the blowback caused by larger military interventions. It would also avoid stoking alarm at home, keeping a threat that kills far fewer Americans than gun violence or heart disease in perspective. 

Not least, although a light-footprint strategy would cost more than disengagement, it would be cheaper than the more aggressive options. It could therefore free up resources to deal with other pressing problems, from climate change to resurgent great-power rivalry. Given these advantages, it is unsurprising that this approach appealed to the Obama administration after the end of the Iraq war and bin Laden’s death.

As the Obama administration discovered, however, a light footprint is no panacea. For one thing, the strategy means relying on unsavory local actors who are wont to do morally appalling things. Nor does it even guarantee success. At best, it would involve enormous persistence merely to contain terrorist organizations and avert disaster; the Israeli government calls its version of the strategy “mowing the grass,” evoking a Sisyphean task. At worst, local partners, without more U.S. support than this option entails, might fail to contain terrorist groups—something that has doomed the strategy in the past. 

Between 2003 and 2011, for instance, Washington spent considerable time and money building up the Iraqi security forces as a counterterrorism partner—only to see them collapse after 2011, when the United States withdrew its troops from Iraq. This allowed ISIS to establish its quasi state, recruit foreign fighters, and direct and inspire attacks. 

Something similar happened in Yemen. The light-footprint approach worked well for a time against AQAP—so well that in 2013 and 2014, the Obama administration touted it as a model for counterterrorism. Yet by early 2015, the Yemeni state and armed forces were crumbling before an externally supported Houthi rebellion, taking down the U.S. counterterrorism mission in the process and allowing AQAP to expand its hold in the country.

The United States cannot cure the pathologies that cause terrorism and so will never eliminate the threat.

The danger of a light-footprint approach, then, is that it may incur some of the costs of action but not do enough to keep the threat under control—and that when it fails, it will require the United States to intervene under less favorable circumstances than before, while also bringing down heavy criticism on the leaders responsible. This is exactly what happened to the Obama administration by 2014–15, causing it to shift to a more aggressive strategy. 


The third—and probably best—option is a beefed-up version of the current strategy: call it “counter-ISIS plus.” It would involve a larger U.S. military commitment than the first two but substantially less than a surge approach. At a minimum, the commitment would approximate that of the Obama administration’s 2016 counter-ISIS campaign, which deployed roughly 5,000 U.S. troops to Iraq and Syria and included thousands more conducting air strikes or other supporting operations in the region. At a maximum, it would approach 20,000 military personnel, deployed to address specific threats from the strongest terrorist organizations and to train and assist regional forces. And crucially, this strategy would go beyond just deploying more troops than a light-footprint approach: it would also allow them to operate more assertively. 

U.S. forces would still conduct drone strikes and other long-distance, limited-liability attacks, but these would form part of larger, more intensive air campaigns involving manned aircraft, forward air controllers, and a broader range of targets. Meanwhile, special operations forces would conduct a steady rhythm of raids to gather intelligence, kill or capture terrorist leaders, and disrupt terrorist organizations. And battalion-size U.S. forces would carry out combat operations on the ground, either independently or in support of regional partners. These might be similar to Operation Anaconda in Afghanistan in 2002, in which over 1,000 U.S. troops and 1,000 Afghan militia forces, supported by other coalition forces, engaged in a fierce battle against al Qaeda and Taliban fighters. Finally, U.S. troops would work with partner forces not just by training and equipping them but also by advising them and accompanying them into battle. These security force assistance missions would continue even after the main campaigns had ended to make sure partner forces remained effective.

Under this approach, the United States would still not attempt to transform Middle Eastern societies, although it would encourage local partners to make political and economic reforms to defang jihadist ideology, and it would use diplomacy and modest economic investments to incentivize those reforms. In the meantime, Washington would seek to militarily defeat, rather than merely contain, extremist organizations. And to do so, it would accept the risk of more American casualties.

A man who fled Mosul in Khazer refugee camp, Iraq, November 2016.
A man who fled Mosul in Khazer refugee camp, Iraq, November 2016.
Mohammed Salem / Reuters

This strategy rests on a diagnosis similar to that underlying the light-footprint approach: that the United States cannot cure the pathologies that cause terrorism and so will never eliminate the threat. Yet this approach is more pessimistic about the dangers of allowing extremist organizations to survive and more optimistic about the chances of militarily defeating them. The United States can achieve significant, if not permanent, military success against terrorists, the thinking goes, by destroying their organizations, killing their leaders and foot soldiers, and leaving them with no safe havens. Knock an opponent down hard enough, in other words, and it will take him a while to get back up.

Indeed, the main advantage of this strategy over less aggressive options is that it would pack a greater punch against terrorist networks while still avoiding large, costly, and politically toxic deployments. By combining a range of tools—airpower, advisers, special operations forces, intelligence, and diplomacy—the United States could destroy the most dangerous terrorist networks and prevent threats that are manageable today from turning into something far deadlier tomorrow. What’s more, providing more robust support to partner forces would help maintain their effectiveness and give the United States greater leverage to moderate counterproductive behaviors such as human rights violations and sectarian abuse, which could help prevent blowback. For example, the local forces with which the United States has partnered to fight ISIS—the Iraqi security forces and the Kurdish peshmerga in Iraq and Arab and Kurdish groups in Syria—have performed better since the United States shifted to its current strategy in late 2014. The experience of the past 15 years suggests that this strategy can work against even fearsome opponents, whether al Qaeda in Afghanistan in 2001–2 or ISIS today. Finally, by striking a balance between doing too much and doing too little, this option would mitigate the political risks of both more passive and more aggressive strategies.

Yet this strategy would also have downsides. It would involve deploying between 5,000 and 20,000 troops at any one time. Even deployments inevitably raise the chances of more American deaths than planners expect. It would also mean spending $5–$20 billion per year—not a prohibitive sum, but far more than more passive options would cost. 

The greatest danger of such a campaign is that it might last indefinitely. Even in the best case, it would require a great deal of time to succeed—witness the glacial pace of the counter-ISIS campaign today. At worst, if terrorism is indeed rooted in the political pathologies of many Muslim societies, then military victories may not stay won unless those pathologies are cured—something that might take more energy and resources than this strategy would provide. 


This point leads to the final option, a surge strategy. This would entail a large, medium- to long-term military deployment similar in size to the surge of 150,000–200,000 troops that the George W. Bush administration committed to the Iraq war in 2007–8, along with proportional economic, diplomatic, and intelligence resources. The United States would aim not only to destroy the most dangerous terrorist organizations wherever they emerged but also to remake the political complexion of the greater Middle East. 

Like the second and third options, this strategy rests on the theory that Middle Eastern terrorism flows from political illiberalism in the Muslim world. But it assumes that the United States must cure the disease, not merely treat its symptoms. Failing to do so, the argument goes, would ensure that new terrorist groups would arise as old ones were defeated. In a world of imperfect intelligence, allowing new threats to survive risks exposing Americans to a catastrophic attack. 

Each of the main options for fighting terrorism has flaws.

This diagnosis suggests a two-step response. First, destroy any terrorist organization capable of global reach, using whatever means necessary, including major military operations featuring tens of thousands of troops. Second, transform the underlying sociopolitical dynamics that drive jihadist ideology. Doing so would require catalyzing political liberalization in the Islamic world, so the United States would have to engage in nation building and democracy promotion in all countries where it had intervened to root out terrorism. 

The allure of this option is that it offers, in theory at least, the chance to win the war on terrorism once and for all. This reflects a crucial insight from the Iraq war. Even if U.S. officials blundered when they chose to invade Iraq, they made just as grave a mistake in committing insufficient troops and resources to Iraqi reconstruction and in pulling U.S. troops out so precipitously in 2011, which jeopardized U.S. soldiers’ hard-won gains. Since half measures and premature withdrawal end only in long-term failure, the logic goes, better to take a shot at winning decisively, despite the extremely high cost.

Yet that cost—which must be borne for many years—is precisely the problem with this strategy. Transforming the politics of the greater Middle East in the ways the United States would want would be a huge challenge under any circumstances. And without a shock the size of 9/11, even a determined U.S. administration would probably lack the political will to sustain the necessary level of spending and deployments—and suffer the resulting casualties—over the long term. The result might be the worst of all worlds: the United States would invest vast resources up-front without the commitment necessary to see the project through. 

This is not the only liability. A surge risks distorting U.S. grand strategy by pouring resources into counterterrorism at the expense of other vital issues, such as climate change, the rise of China, and a revanchist Russia. What’s more, putting more skin in the game might just encourage other countries to free-ride on U.S. efforts. Finally, a strategy that relies on large military interventions in the greater Middle East risks provoking all the blowback that a lighter footprint would avoid. Terrorists would attack U.S. forces, whose presence in the Middle East would validate the jihadist narrative of a U.S. crusade against Muslims.

Whatever its attractions, then, a surge strategy would face daunting, probably insurmountable obstacles. No wonder, then, that no major candidate in the 2016 presidential race advocated anything close to this option—and that Trump has explicitly taken this sort of nation building off the table. 

People run after a coalition airstrike hits the Tahrir neighborhood of Mosul, Iraq, November 2016.
People run after a coalition airstrike hits the Tahrir neighborhood of Mosul, Iraq, November 2016.
Goran Tomasevic / Reuters


The tragedy of the United States’ war on terrorism is that it has no clean solution. Each of the four main options for fighting terrorism has flaws, in some cases crippling ones. But the United States must have a strategy. So which one should it pick? U.S. officials should discard the two extremes, disengagement and surge, on pragmatic grounds. Disengaging would bet the house on an untested hypothesis—that pulling back would significantly reduce the terrorist threat—which would leave the United States terribly vulnerable if it proved false. Few prudent politicians would hazard their careers on such a wager. The surge approach, for its part, would be enormously difficult to execute, and because of its extremely high cost, politicians would likely lack the stamina to stay the course. 

That leaves the two middle-ground options: a light footprint and counter-ISIS plus. Of these, the former has a lousy recent track record, as ISIS emerged and the United States’ position deteriorated dramatically the last time this strategy dominated U.S. policy. Employing it would risk starting a cycle in which a U.S. pullback causes the threat to increase, compelling the United States to intervene again under worse circumstances than before. The strategy thus also occupies a precarious political footing: it would probably not survive a repetition of the type of attacks that occurred in late 2015 and 2016, when ISIS-inspired shooters killed 63 people in San Bernardino and Orlando.

So the last strategy standing is counter-ISIS plus. True, it has real problems and risks doing no more than failing at greater expense than the light-footprint approach. But it succeeded both when the Bush administration and when the Obama administration employed it aggressively, and it could well eliminate the worst aspect of the terrorist threat—the existence of breeding grounds for mass-casualty attacks—if pursued consistently. The cost of doing so would hardly be trivial, but a wealthy superpower could manage it. Additionally, although this approach would probably not produce exceptional performance from U.S. partners, it might help them do well enough to limit U.S. costs over the long run. Finally, despite Trump’s harsh critiques of the Obama administration’s campaign against ISIS, this approach is probably the most politically salable. 

The Trump administration should thus take this variant of the strategy that the Obama administration had built up to by 2016 as its guide. It is not perfect and will not end the war on terrorism anytime soon. But it may give the United States a minimally acceptable level of security in a dangerous struggle.

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  • PETER FEAVER is Professor of Political Science and Public Policy at Duke University. HAL BRANDS is Henry A. Kissinger Distinguished Professor of Global Affairs at Johns Hopkins University’s School of Advanced International Studies and a Senior Fellow at the Center for Strategic and Budgetary Assessments.


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