Syria is a hard one.

The arguments against the United States’ taking a more active role in ending the vicious three-year-old conflict there are almost perfectly balanced by those in favor of intervening, especially in the aftermath of the painful experiences of the wars in Afghanistan and Iraq.

The cons begin with the simple fact that the United States has no interests in Syria itself. Syria is not an oil producer, a major U.S. trade partner, or even a democracy.

Nevertheless, the rationale for more decisive U.S. intervention is gaining ground. As of this writing, the crisis in Syria had claimed more than 170,000 lives and spilled over into every neighboring state.

The havoc is embodied most dramatically in the Islamic State of Iraq and al-Sham, or ISIS, a Sunni jihadist organization born of the remnants of al Qaeda in Iraq. After regrouping in Syria, ISIS (which declared itself the Islamic State in late June) recently overran much of northern Iraq and helped rekindle that country’s civil war.

ISIS fighters take part in a military parade along a street in northern Raqqa province on June 30, 2014. Reuters ISIS is now using the areas it controls in Iraq and Syria to breed still more Islamist extremists, some of whom have set their sights on Western targets. Meanwhile, Syria’s conflict is also threatening to drag down its other neighbors -- particularly Jordan, Lebanon, and Turkey, where the influx of nearly three million refugees is already straining government budgets and stoking social unrest.

After resisting doing so for three years, the White House is now scrambling to expand its role in the turmoil. In June, U.S. President Barack Obama requested $500 million from Congress to ramp up U.S. assistance to moderate members of the Syrian opposition (such assistance has until recently been limited to a covert training program in Jordan).

Yet at every stage of the debate on Syria, the administration has maintained that the only way to decisively ensure the demise of the Assad regime is to deploy large numbers of ground troops.

But there is, in fact, a way that the United States could get what it wants in Syria — and, ultimately, in Iraq as well — without sending in U.S. forces: by building a new Syrian opposition army capable of defeating both President Bashar al-Assad and the more militant Islamists.

The United States has pulled off similar operations before and could probably do so again, and at far lower cost than what it has spent in Afghanistan and Iraq.

Considering the extent to which the Iraqi and Syrian civil wars have become entwined, such a strategy would help secure U.S. interests throughout the Middle East. Indeed, despite its drawbacks, it has become the best option for the United States and the people of Syria and the region.

President Obama has been reluctant to entangle U.S. forces in the Syrian conflict. Kevin Lamarque/Reuters

Pick Your Battles

Given the powerful arguments against a greater U.S. role in Syria, any proposal to step up U.S. involvement has to meet four criteria.

First, the strategy cannot require sending U.S. troops into combat. Funds, advisers, and even air power are all fair game -- but only insofar as they do not lead to American boots on the ground.

Second, any proposal must provide for the defeat of both the Assad regime and the most radical Islamist militants, since both threaten U.S. interests.

Any proposal must provide for the defeat of both the Assad regime and the most radical Islamist militants — both threaten U.S. interests.

Third, the policy should offer reasonable hope of a stable end state. Because spillover from Syria’s civil war represents the foremost security concern, defeating the regime while allowing the civil war to continue — or even crushing both the regime and the extremists while allowing other groups to fight on — would amount to a strategic failure.

There are no certainties in warfare, but any plan for greater U.S. involvement must at least increase the odds of stabilizing Syria.

Finally, the plan should have a reasonable chance of accomplishing what it sets out to do. Washington must avoid far-fetched schemes with uncertain chances of success, no matter how well they might fit its objectives in other ways. It should also properly fund the strategy it does select. Announcing a new, more ambitious Syria policy but failing to give it an adequate budget would be self-defeating, convincing friend and foe alike that the United States lacks the will to defend its interests.

Every proposal so far for greater U.S. involvement in Syria has failed to satisfy at least one of these criteria. The Obama administration’s new bid to expand training and equipment aid for the moderate opposition is no exception.

Over time, supplying advanced antiaircraft and antitank weapons to the rebels, as Washington intends, would make victories costlier for the Assad government. But even large quantities of such arms are unlikely to break the stalemate.

A Free Syrian Army fighter takes cover during clashes with Syrian Army in the Salaheddine neighborhood. Goran Tomasevic/Reuters During the Soviet war in Afghanistan in the 1980s, for example, mujahideen fighters armed with U.S.-supplied Stinger antiaircraft and Milan antitank missiles inflicted heavy losses on Soviet tanks and helicopters but failed to score tactical battlefield gains.

Moreover, unlike the Soviet Union, which was fighting a war of choice in Afghanistan (and could simply walk away), the Assad regime is waging a war for survival. Heavier equipment losses are unlikely to force it to capitulate, especially if it continues to win individual battles.

More problematic, the current strategy does not ensure a stable end state. Providing weapons and limited training to the rebels will simply improve their ability to kill.

It will not unite them, create a viable power-sharing arrangement among fractious ethnic and sectarian communities, or build strong government institutions.

These same shortfalls led to Afghanistan’s unraveling once Soviet forces withdrew; the victorious mujahideen soon started fighting one another, which eventually allowed them all to be crushed by the Taliban.

Army Strong

Studying past cases of American military support suggests an alternative course: the United States could create a new Syrian military with a conventional structure and doctrine, one capable of defeating both the regime and the extremists.

A decisive victory by this U.S.-backed army would force all parties to the negotiating table and give the United States the leverage to broker a power-sharing arrangement among the competing factions. This outcome would create the most favorable conditions for the emergence of a new Syrian state: one that is peaceful, pluralistic, inclusive, and capable of governing the entire country.

To get there, the United States would have to commit itself to building a new Syrian army that could end the war and help establish stability when the fighting was over. The effort should carry the resources and credibility of the United States behind it and must not have the tentative and halfhearted support that has defined every prior U.S. initiative in Syria since 2011.

The U.S. could recruit foreign fighters to join its army against Assad. Flickr/Thierry Ehrmann If the rest of the world believes that Washington is determined to see its strategy through, more countries will support its efforts and fewer will oppose them.

Success would therefore require more funding — to train and equip the new army’s soldiers — and greater manpower, since much larger teams of U.S. advisers would be needed to prepare the new force and guide it in combat operations.

Recruiting Syrian army personnel would be the first task. These men and women could come from any part of the country or its diaspora, as long as they were Syrian and willing to fight in the new army.

They would need to integrate themselves into a conventional military structure and adopt its doctrine and rules of conduct. They would also have to be willing to leave their existing militias and become reassigned to new units without regard for religion, ethnicity, or geographic origin.

Loyalty to the new army and to the vision of a democratic postwar Syria for which it would stand must supersede all other competing identities.

Loyalty to the new army and to the vision of a democratic postwar Syria for which it would stand must supersede all other competing identities.

The strategy’s most critical aspect would be its emphasis on long-term conventional training. The program would represent a major departure from the assistance Washington is currently providing the opposition, which involves a few weeks of coaching in weapons handling and small-unit tactics.

The new regimen, by contrast, should last at least a year, beginning with such basic training and then progressing to logistics, medical support, and specialized military skills. Along the way, U.S. advisers would organize the soldiers into a standard army hierarchy. Individuals chosen for command positions would receive additional instruction in leadership, advanced tactics, combined-arms operations, and communications.

Because the existing Syrian opposition is hobbled by extremism and a lack of professionalism, vetting all new personnel would be crucial. History shows that the only effective way to do this is for the U.S. advisers to work with the recruits on a daily basis. That would allow the advisers to gradually weed out the inevitable bad seeds -- radicals, regime agents, thugs, and felons -- and promote the good ones.

Since training the first cadre of fighters (a task that the CIA would likely handle) would require security and freedom from distraction, it would be best to start it outside Syria. Possible training sites could include Jordan, where the United States is already providing some aid to the rebels, and Turkey.

Both countries have strongly lobbied Washington to widen its support for the Syrian opposition. Yet both would probably demand compensation for hosting big new base camps.

U.S. President Barack Obama meets with Jordan's King Abdullah at Sunnylands in Rancho Mirage, California February 14, 2014. Kevin Lamarque/Reuters Jordan already receives about $660 million in U.S. aid per year, and in February 2014, the White House pledged an additional $1 billion in loan guarantees to help the country with its refugee burden. Washington could offer to continue such aid in return for cooperation with its new strategy.

In addition to being trained and organized like a conventional military, the new force must be equipped like one. Washington would need to provide the new army with heavy weapons, including tanks, armored personnel carriers, artillery, and surface-to-air missiles -- vital tools for eliminating the regime’s current advantage in firepower.

The new army would also need logistical support, communications equipment, transport, and medical gear to mount sustained offensive and defensive operations against the regime.

The Road to Damascus

This new Syrian army would eventually move into Syria, but only once it was strong enough to conquer and hold territory. For that, it would need to reach a critical threshold of both quantity and quality.

It would be unwise to send the new army into the maelstrom of Syria until it could field at least two or three brigades, each composed of 1,000 to 2,000 soldiers. Yet more important, these formations should go into battle only once they have developed the unit cohesion, tactical skills, leadership, and logistical capabilities necessary to beat the regime’s forces and any rival militias. And when it does cross into Syria, the army should do so accompanied by a heavy complement of U.S. advisers.

Syrian refugees from the town of Qara gather around a fire to keep themselves warm in a Syrian refugee camp on the Lebanese border town of Arsal, in eastern Bekaa Valley. REUTERS Even after the force made its first significant territorial gains, it would have to keep growing. Its ultimate task — securing control of the entire country by crushing all actors that challenge it — would require several hundred thousand soldiers to complete. But the launch of military operations would not have to wait until the army could field that many fighters. Quite the contrary: it could still recruit and train most of its soldiers after its first brigades made their initial advance.

Once the soldiers began to secure Syrian territory, their leaders would need to quickly restore law and order there. That would mean allowing international humanitarian organizations to return to areas that are currently off-limits and protecting their staff while they deliver aid. It would also require the establishment of a functional, egalitarian system of governance.

The vast majority of Syrians want nothing to do with either Assad’s tyranny or the fanaticism of his Islamist opponents. As in every intercommunal civil war, the population is likely to rally behind any group that can reinstate order. The new army should thus be ready from the outset to meet people’s needs in every city and village it wins back, which would also distinguish it from its rivals.

Free Syrian Army fighters help a fellow fighter who was wounded during what the FSA said was an airstrike by forces loyal to Syria's President Bashar al-Assad in the southern Idlib countryside July 9, 2014. Khalil Ashawi/Reuters Once the new army gained ground, the opposition’s leaders could formally declare themselves to represent a new provisional government. The United States and its allies could then extend diplomatic recognition to the movement, allowing the U.S. Department of Defense to take over the tasks of training and advising the new force — which would now be the official military arm of Syria’s legitimate new rulers.

Lessons from other countries demonstrate that postwar governments are most durable when they grow from the bottom up. When they are imposed from the top down, as was the case in Iraq in 2003, the outcomes can range from bad to catastrophic. But allowing the new government to take shape organically in Syria would take years.

In the meantime, areas controlled by the U.S.-backed army would require a provisional authority — ideally, a special representative of the UN secretary-general who would retain sovereignty until a new government was ready.

If history is any guide, as the new force started to beat back both the regime and the Islamist extremists, fairly administer its territory, and prove to the world that the United States and its allies were determined to see it succeed, growing numbers of Syrians should flock to its cause. This surge of public support would generate more volunteers for the army and a groundswell of momentum for the opposition movement, factors that have often proved decisive in similar conflicts.

One of the most baleful legacies of protracted civil wars is the difficulty of creating stable political systems once the fighting ends.

Stable peace in the wake of intercommunal strife requires a pluralistic system with strong guarantees of minority rights. Such a system, in turn, rests on an army that is strong, independent, and apolitical.

Postwar Syria would need this kind of military culture to reassure all its communities that whoever holds power in Damascus would not once more turn the security forces into agents of oppression. The best way to ensure that the army upheld these principles would be to ingrain them in its institutional culture from the very start, through the long-term process of military socialization.

Iraq offers both a powerful example and a critical warning in this regard. On the one hand, by 2009 the United States had succeeded there in building a military that, although only modestly capable, was quite independent and apolitical.

Just three years earlier, the country’s security forces had been a discredited and inept institution and a source of fear for most Iraqis. Similar to the Syrian opposition today, the Iraqi army had been overrun by criminals, extremists, militiamen, and incompetent, poorly equipped fighters. Yet a determined U.S. program transformed the force, making it a welcomed, even sought after, enforcer of stability across the country.

In 2008, for example, mostly Sunni army brigades were hailed as liberators by the Shiites of Basra when they drove out the Shiite militia Jaish al-Mahdi. A key factor in this transformation was rigorous training of the kind here proposed for Syria, which allowed U.S. advisers to vet local personnel.

Prime Minister Nouri al-Maliki disappointed Washington by politicizing the army and oppressing Sunni muslims. REUTERS/Jonathan Ernst On the other hand, a strong independent army often draws the suspicion of ruthless local politicians who try to subvert or politicize it. That is precisely how Prime Minister Nouri al-Maliki turned the Iraqi military back into a sectarian militia after Washington disengaged. The resulting decline in skill and morale explains why four Iraqi army divisions collapsed in the face of the ISIS offensive in June, and why many Sunnis threw in their lots with ISIS against Maliki.

The lesson for Syria is that it’s not enough to merely bring a new army into existence and help it win the war. If the United States wants to see the country develop into a stable new polity, it will have to keep supporting and shepherding the new Syrian military for some years thereafter, albeit at declining levels of cost and manpower.

Even though the United States eventually gave up on Vietnam, it did enjoy considerable success rebuilding the South Vietnamese army from 1968 to 1972. Horst Faas/AP Winning the Peace

The biggest question about this ambitious proposal, of course, is, can it work? Although wars are always unpredictable, there is more than enough historical evidence to suggest that this approach is entirely plausible — and in fact better than any other option for intervention.

For example, even though the United States eventually gave up on Vietnam, it did enjoy considerable success rebuilding the South Vietnamese army from 1968 to 1972, after U.S. neglect and Vietnamese mismanagement had left it politicized, corrupt, and inept.

Although that force continued to face many problems, it improved so much that it managed to halt the North’s invasion during the Easter Offensive of 1972. South Vietnamese fighters did enjoy the backing of extensive U.S. air power and legions of U.S. advisers, but four years earlier, few had believed them capable of such a feat even with that kind of support.

Then there is the dramatic transformation of the Croatian army that NATO achieved during the 1992–95 Bosnian war, a conflict precipitated by ethnic and territorial tensions triggered by the dissolution of Yugoslavia. The fledgling Croatian force, which was supporting the Bosnian Croats against Serbian forces, had started out hapless and incompetent in the opening months of the war.

NATO achieved a dramatic transformation of the Croatian army during the 1992–95 Bosnian war. Wikimedia Commons/Lt Stacey Wyzkowski/www.dodmedia.osd.mil In three years, the West’s provision of training and supplies, coupled with the determination of the Croatian fighters, was enough to remake the army into an efficient fighting machine able to mount a series of combined-arms campaigns that forced Serbia to the negotiating table. (This example is particularly apt for Syria because Serbia’s forces were far more formidable than Assad’s.)

Iraq’s history, meanwhile, illustrates both the ability of the United States to build a relatively capable indigenous force in just a few years largely from scratch and the perils of abandoning it to an immature political system.

In each of these cases, the factor that mattered most was commitment on the part of Washington. Where and when the United States has proved willing to make its strategy work -- in Vietnam, Bosnia, even Iraq -- it has succeeded. But where it abandoned its commitments, its progress rapidly came undone.

U.S. experience in Bosnia and Iraq also points to an effective tactic for preventing a bloodbath after the new Syrian army wins. In both those countries, the United States built up a force that was clearly capable of defeating its rivals, but then Washington was able to prevent it from taking that final step.

The U.S.-backed groups fought well enough to convince their enemies of the necessity to compromise on a power-sharing arrangement. At the same time, U.S. pressure ensured that the winners accepted something less than total victory.

Past performance is no guarantee of future success

Past performance is no guarantee of future success, of course, and each historical analogy differs from Syria in important ways.

The South Vietnamese army’s improved performance failed to forestall its collapse once it lost U.S. air cover.

Croatia in the early 1990s was a proto-state fighting another proto-state, Serbia.

Iraqi security force benefited from a massive U.S. ground presence that went well beyond what the proposed plan envisions for Syria.

The prospect that a new Syrian army could be created from scratch and lack the power of a state behind it should give policymakers pause, but these problems should not be deal breakers. The Northern Alliance (the group that helped topple the Taliban in Afghanistan in 2001) and the Libyan opposition each managed to prevail with no Western support beyond advisers and air power; they certainly never enjoyed the backing of a proto-state such as Croatia.

Of course, Assad’s troops are also more capable today than were either the Taliban’s forces in Afghanistan or Muammar al-Qaddafi’s army in Libya. But strong as the Syrian military may seem in a relative sense, it is hardly a juggernaut, having performed miserably in every war since 1948 and having fought only marginally better than the very lackluster opposition since 2012.

How long would it take to implement this plan? The history of similar operations in Bosnia, Afghanistan, Iraq, and Libya indicates that the United States would need one to two years to prepare the first few brigades. After their initial foray into Syria, the growing army would likely need another one to three years to defeat the regime’s forces and other rivals. That suggests a two- to five-year campaign.

It's going to take a long time to rebuild Syria after the fighting ends. REUTERS/Ghassan Najjar Once it attained a peace deal, the new army would have to reorganize itself into a traditional state security apparatus. It might have to further expand its ranks in order to meet Syria’s long-term security needs, including the defeat of residual terrorist elements.

This stabilizing role would take years longer but would be far less demanding than fighting the Assad regime, especially if the United States kept up its support for Syria’s new institutions and its economic and political reconstruction.

Critics will inevitably argue that this road map for Syria is infeasible today, coming too late to make a difference. Yet analogous arguments have proved wrong in the past. In March 2005, for example, I gave a briefing on Iraq to a small group of senior U.S. officials, presenting the strategy I had been advocating since early 2004: a shift to true counterinsurgency operations, an effort to reach out to the Sunni tribal leaders of western Iraq, the addition of thousands of U.S. forces, and a bottom-up process of political reform to encourage power sharing.

My audience responded that although this plan might have worked in 2003 or even 2004, by 2005 Iraq was simply too far gone. Yet what I was prescribing was the very strategy that General David Petraeus and Ryan Crocker, the U.S. ambassador to Iraq, would employ two years later -- and that would turn the tide of the conflict.

Likewise, there is no reason to believe that it’s too late for Syria.

U.S. air support may prove unnecessary if the army can be made strong enough. AFP The civil war there will not end anytime soon, despite the fact that expanded Iranian and Russian assistance have allowed Assad loyalists to make significant gains.

The most probable scenario is that the regime’s advances will prove limited and the resources flowing to the rebels from their foreign backers will cause a stalemate. Syria will burn on, while U.S. officials continue telling themselves that the time for action has passed.

Even if Washington adopted this course of action, many more Syrian lives would be lost before it could succeed. The only way to save those lives, however, would be to deploy U.S. ground forces -- a proposal that, given the American public’s sentiment, is a nonstarter. Barring boots on the ground, the approach described here is the best chance to avoid hundreds of thousands of additional casualties.

Support from the Skies

Another key question is whether the plan would require U.S. air power, since an air campaign would make this strategy far more expensive in both financial and diplomatic terms. At least one case, the Bosnian war, suggests that U.S. air support may prove unnecessary.

During that conflict, it was a Croatian (and Bosnian) ground assault, undertaken with barely any Western air cover, that made the difference. Although NATO flew 3,515 sorties during the conflict, none was in direct support of the Croatian forces, and most of the targets were unrelated to the ground fighting.

Moreover, the unclassified CIA history of the war concluded that the NATO air strikes contributed only modestly to securing Serbian acquiescence to the Dayton peace accords; Croatian battlefield victories mattered far more.

Most of the other historical evidence, however, indicates that U.S. air support would be needed. In Afghanistan in 2001 and Libya in 2011, Western air power paved the way for the opposition victories. Looking further back in time, even after the South Vietnamese army matured enough to operate without U.S. ground support, it remained dependent on massive U.S. air assistance -- albeit while battling a foe much tougher than the Assad regime.

Nevertheless, the fact that the proposed strategy could require air power does not mean that the American public will necessarily oppose it. Public opinion surveys in the mid-1990s, during the Bosnian war, showed firm and consistent opposition to U.S. intervention, even if undertaken multilaterally.

Yet those same polls reported considerably higher support for air operations. Likewise, few Americans objected when the Obama administration contributed U.S. air forces to the NATO air campaign in Libya in 2011.

Few Americans objected when the Obama administration contributed U.S. air forces to the NATO air campaign in Libya in 2011.

Beyond air power, two other variables would heavily influence the ultimate cost of the strategy proposed here: how much Washington spent on the new Syrian army, and whether it could convince its allies to shoulder a part of the burden.

Given the costs of similar past operations, one can reasonably expect the new fighting force to require $1–$2 billion per year to build. The United States would need to budget an additional $6–$20 billion per year for air support and perhaps another $1.5–$3 billion per year for civilian aid.

Adding these sums together yields a total operating budget of $3 billion annually for two or three years at the lower end of the price scale.

If an air campaign on the scale of that in Bosnia, Afghanistan, or Libya were required, the annual price would rise to roughly $9–$10 billion for as long as the fighting continued. And if the United States were forced to provide twice as much air power as it did in those earlier wars, the cost could reach $18–$22 billion per year.

Following a political settlement, Washington’s continued support for the new government would probably require $1–$5 billion in civilian and security assistance annually for up to a decade. By comparison, Afghanistan cost the United States roughly $45 billion a year from 2001 to 2013, and Iraq, about $100 billion a year from 2003 to 2011.

Of course, the numbers would come down considerably if the United States won financial support from its allies in Europe and the Middle East, especially the Persian Gulf states. For years, Gulf leaders have insisted in private that they would fund most or all of such an effort. And they have paid for similar operations in the past.

Saudi Arabia could prove a useful ally in bankrolling a potential Syrian campaign. Pablo Martinez Monsivais/AP Saudi Arabia heavily supported the covert U.S. campaign against the Soviet Union in Afghanistan and, along with Kuwait and other Gulf states, the U.S. operations during the Gulf War. Gulf leaders also threw their weight behind the U.S. decision to intervene in Libya.

There is no question that these states see the outcome of the Syrian conflict as vital to their interests; they have already spent billions of dollars backing various Syrian militias. So they would likely support the scheme outlined here -- although Washington should gauge their interest before deciding whether to pursue it.

Raising the Bar

If the Obama administration does decide to build a Syrian army, it should do so with its eyes open, for the strategy would entail some risk of escalation.

Few, if any, wars work exactly as planned without incurring unexpected costs, and some turn out to be far more expensive, messy, and deadly than anticipated.

Obama meets with ISAF leaders in Afghanistan. AP/ Evan Vucci Afghanistan and Iraq are both cases in point, and they also demonstrate that a country typically gets the worst outcome when it prepares for nothing but the best. If the United States pursued the strategy proposed here, it would need to be prepared to lose some American lives. U.S. pilots could be shot down and U.S. advisers could be wounded, killed, or captured.

The Assad regime could also launch missile strikes against U.S. allies in retaliation or mount terrorist attacks abroad. Syria’s allies Iran and Hezbollah could respond as well, likely by attacking U.S. advisers, just as they did U.S. troops in Iraq.

The fear of Washington’s counterattack could deter Tehran from staging a more direct assault but might be insufficient to scare off Hezbollah, since the fall of the Assad regime would imperil Hezbollah’s very existence. And no matter what country ultimately hosted the new Syrian army during the early stages of its development, that country would need guarantees that the United States would help defend it against enemy retaliation.

Finally, the new Syrian army could still lose the war. Given the limited capability of Assad’s forces and the previous successes of Western air power in similar circumstances, such a scenario seems unlikely, but it should not be ruled out.

The same goes for a slightly more realistic worry: that the opposition would conquer the country but then fail to secure it. The new Syrian army would then continue to face a grueling and destabilizing battle with extremists and insurgents while struggling to establish law and order, a challenge that undermined postwar governments in both Afghanistan and Libya.

In all these scenarios, the pressure on the United States to escalate its involvement would increase. The strategy outlined here is designed to minimize this risk, but it cannot eliminate it.

The strategy outlined here is designed to minimize this risk, but it cannot eliminate it.

No one should embrace this approach without recognizing that it could at some point confront Washington with the difficult choice between doubling down and walking away.

The Costs of Inaction

Since the fall of Mosul in June 2014, the Syrian and Iraqi civil wars have become entangled. Any strategy to deal with one must also deal with the other. The region’s sectarian fault lines complicate matters further.

In Syria, the Sunni majority is in revolt; in Iraq, the Sunni minority is. In both countries, the United States is seeking to separate the moderate Sunni opposition from more radical groups, such as ISIS. But only in Syria does it aim to depose a Shiite regime. In Iraq, Washington hopes to remain on good terms with the Shiite-dominated government, even as it insists that Baghdad enact immediate and far-reaching reforms.

The strategy proposed here would serve U.S. interests in both countries. Although the contemplated new Syrian army should be neutral, it would inevitably be dominated by Sunnis. Its victories over both the Shiite-dominated Assad regime and the Islamist militants in Syria would make it a model for Iraq’s moderate Sunni tribes.

A militant Islamist fighter waves a flag and gestures as he takes part in a military parade along the streets of northern Raqqa province June 30, 2014. REUTERS These groups would be key to defeating ISIS, just as their support proved crucial for the U.S. troop surge in Iraq in 2007–8. Decisive U.S. support for the Syrian offshoots of those Iraqi tribes -- coupled with Washington’s commitment to build the kind of inclusive, pluralistic, and equitable state in Syria that moderate Sunnis seek in Iraq -- could help turn Sunnis across the region against ISIS and its ilk.

Events in Iraq have starkly demonstrated the costs of inaction. Whatever choice the United States makes, it should not make it in the mistaken belief that there is no plausible strategy for victory at an acceptable cost.

The United States can end the Syrian civil war on its own terms and rebuild a stable Syria without committing ground troops. Doing so could take a great deal of time, effort, and resources.

It will certainly take the will to try.