But securing borders can require large numbers of troops. Borders have physical and political components. Neighboring states’ interests and their own capacity for security will determine the difficulty. So will terrain and internal Syrian security considerations. Troops would also need excellent intelligence and training. But Syria’s army is in disarray, and much of its officer corps will (or should) be purged if Assad goes, though Iraq has taught us to avoid a wholesale dissolution of the military, as Secretary of Defense Leon Panetta recently noted in an interview with CNN. This also holds true for Syria’s police force. Purges of Syria’s uniformed services—viewed by many within Syria as little more than an Alawite militia—would leave an immediate vacuum. Given the societal schisms caused and exacerbated by the conflict, an “impartial” outside role may help reassure communities and ward off dangerous cycles of violence.

Syria’s armed forces still do one valuable thing: secure Syria’s chemical-weapons stockpiles. Even though chemical weapons are less dangerous than conventional weapons in most cases, their psychological impact is massive. Should Assad’s regime fall and the army collapse with it, securing these weapons would be a vital task for outside forces.

Protecting borders, securing chemical-weapons caches and fighting criminality could require sizable external forces. RAND studies on stabilization operations find average force-to-population ratios ranging from 2:1000 to 13:1000, depending on the levels of violence, ambition of objectives and number of contested areas. For Syria’s population of more than twenty-two million, this could mean a range of 44,000–286,000 troops and will probably be on the larger end given the myriad problems there. Of course, force-sizing considerations depend largely on the percentage of population significantly affected and the amount of the country left vulnerable to violence when the regime falls.

Disarmament, demobilization and reintegration (DDR) will be difficult, yet failure to do these things could prove dangerous. Tribal and sectarian interest in settling scores and redistributing power will make fighters reluctant to lay down arms, as will fear of retribution. Unemployment also could prove dangerous. With nothing to do once fighting subsides and before the economy restarts, battle-hardened fighters must be effectively and productively engaged.

DDR efforts must be coordinated with transitional-justice efforts. A properly constituted court system to try those responsible for atrocities could forestall temptations for former victims to settle matters on their own. However, rushing to put large numbers of individuals on trial or conducting a mass purging of government officials such as in Iraq can be similarly destabilizing. The two objectives—stability and accountability—are mutually supportive, but without coordination one effort can undermine the other.

The international community can provide near-term support through forums such as truth and reconciliation commissions. It also can assist with arbitration if it becomes unclear who is the victim or the perpetrator. Though the United States is clearly rooting for the opposition, and Assad’s forces and paramilitary shabiha are committing the bulk of the killing of civilians, the atrocities are not one-sided, and rebel reprisals may increase as the war drags on.

An international presence in Syria can help discourage secessionism—a danger that can spread across borders and, for that reason, invite meddling from neighboring states. Syria’s Kurds could seek to secede not because the demand for their own state is overwhelming but simply because the Syrian state is dysfunctional and denies them just rights. They may also believe that Iraqi and Turkish Kurds, or even sympathetic governments, can help their quest. Outside powers, by providing security and preventing foreign meddling, can dampen this enthusiasm.

The most pressing initial need for aid will be humanitarian assistance. This also is likely to overwhelm any remaining or nascent governmental capacity. The need for shelter, food and health care will be most acute with internally displaced populations and refugees. Current UN figures estimate over 2.5 million people need assistance within Syria’s borders, while over two hundred thousand have fled the country. Many will return to destroyed homes and livelihoods, throwing them at the mercy of external support.

Outsiders can also help economically—and will be expected to do so. A provincial-reconstruction-team member in Iraq commented in conversation on the challenges she observed on the job, saying, “Democracy does not mean free electricity”—yet this was the expectation she routinely encountered. As the most immediate security and humanitarian needs subside, expectations will grow apace. Restoring—or, more accurately, establishing for the first time—a real economy will be an important part of reconstruction as well as longer-term development efforts. A corollary is the need to manage expectations. In Iraq, when expectations were not met the result was anger and frustration.

Finally, outside powers also can offer expertise for the myriad problems any new regime would face. Syria’s government always functioned poorly, and many of the more apolitical and competent civil servants will have fled. Whether it is designing a constitution, rebuilding the electric grid or training military forces to defend borders, the United States and its allies can help the Syrians.

THE UNITED States is far from ready, politically and institutionally, to bear the burden of helping Syria. But the United States has several key strengths when it comes to state building. Perhaps most significant is its long history of involvement in such missions, in particular using the U.S. military. From the Mexican-American and Spanish-American wars through both world wars, the military conducted postconflict reconstruction and military government, albeit, as historian Earl Ziemke noted, as “a kind of reluctant afterthought.” Since the end of the Cold War, the tempo has increased. A 2007 RAND study found the United States launching a new stability operation roughly every other year, while UN peacekeeping missions increased from once every four years to once every six months. Afghanistan and Iraq also have offered painful experiences that generated tremendous study. Coordination of diplomatic, development and defense assets is better, particularly at operational and tactical levels. For U.S. civilian agencies (with the exception of USAID and its operationally focused culture), these skills present a new kind of “operational diplomacy.”

Another significant improvement in U.S. capabilities is the creation of stabilization and reconstruction committees. In 2004, the State Department created the Office of the Coordinator for Reconstruction and Stabilization, followed last year by the Bureau of Conflict and Stabilization Operations. Together with the Defense Department’s recent embrace of stability operations, the U.S. executive branch has undertaken notable, if limited, efforts to develop and maintain state-building capabilities.

Still, the U.S. government remains plagued with structural shortcomings in state building. There remain indications of failure to institutionalize lessons learned from Afghanistan and Iraq. The government seems unsure of what its role in state building can or should be.

Civilian capabilities remain particularly weak. One reason discussion of alternative courses often swings between doing nothing and military intervention is the persistent absence of a robust nonmilitary capability. The underlying premise in Iraq was that the military would stabilize the country and then hand the mission over to civilians for reconstruction, but the handoff never occurred. Civilian organizations dedicated to stabilization and reconstruction materialized too late. Beltway turf battles do not help either; the State Department’s powerful regional bureaus refused to give the predecessor organization to the Bureau of Conflict and Stabilization Operations control of any missions, thus contributing to its demise.

Although planning and coordination have improved, weaknesses remain. How early and how effectively executive agencies engage each other in the planning process is still largely personality-driven, and plans are closely held. The biggest lesson from Iraq is the imperative to plan early and inclusively. Many of the missteps and breathtaking oversights following the Iraq invasion are attributed to flawed plans that failed to take into account critical outside perspectives.

Another potential pitfall is in dispensing aid. In Iraq, aid dollars flowed through a single source—the U.S. government—with substantial delays reaching target recipients or achieving desired economic conditions. Afghanistan saw a web of donor countries and nongovernmental organizations achieve similarly poor results, sometimes undermining the Afghan governmental controls. The danger in Syria is that dollars could be used in ways that could put its economic viability further out of reach or create unsustainable expectations. A Senate report last year found that 97 percent of Afghan GDP derived from military spending and international support. Without that support, it concluded Afghanistan could suffer “a severe economic depression.”

Even when presidents generate political and public support for intervention, the United States historically has lacked the will to stay committed. Without strong support for war, domestic tolerance for casualties is near zero, and interest in spending large sums on foreign development has never been strong. The idea that nation building can be done on the cheap largely has been debunked, and the crippling bills racked up in Afghanistan and Iraq make for a nasty reality. Fatigue and overextension resulting from those conflicts make the likelihood of domestic support for a long, costly engagement nearly nil. Pew Research Center polls found only 25 percent of Americans believed the United States should intervene in Syria (with only 14 percent calling for deploying troops), and support would surely be less for a messy and expensive state-building effort.