In our last Foreign Affairs article (“Humanitarian Intervention Comes of Age,” November/December 2011), we noted that armed conflicts have generally become shorter, less intense, and more localized than they were in the past. As the Uppsala Conflict Data Program in Sweden has documented, the number of battle-related deaths worldwide has been lower in each of the past ten years than in any in any previous year since the 1950s. (2012 data have not been released, but are expected to maintain the pattern.) Such improvements are partially thanks to the development of international norms about violence, including the UN-approved doctrine of the responsibility to protect (R2P), which holds that the international community is prepared to take action to protect civilians -- by force, if necessary -- when national governments fail to do so.

The international community has also developed better tools for managing and preventing conflicts. Peace agreements are more effective and less likely to break down. Transitional justice institutions, including the International Criminal Court, the ad hoc tribunals on Yugoslavia, Rwanda, and Sierra Leone, and a broad range of domestic tribunals, have done a better job of championing human rights than ever before. And, finally, as demonstrated in Libya, in 2011, military intervention has at times prevented civilian deaths.

Every rule, however, has an exception. In this case, it is the bloody, sectarian civil war in Syria, which shows no sign of abating. In the two years since the conflict began, an estimated 70,000 people have died, and more than three million have been displaced from their homes. Each side enjoys the backing of outside powers, and the UN Security Council has failed to pass meaningful resolutions laying out a blueprint for ending the conflict.

In many ways, the international community’s inability to stop the escalating violence in Syria is reminiscent of the deadlock and vacillation over intervening in Bosnia in the 1990s. In that case, nearly 100,000 people died before an effective international response helped end the conflict, in 1995. Given international disagreement over Syria, some observers argue that little has changed since then, and that R2P is a meaningless doctrine invoked only when the interests of great powers align. In the face of mounting fatalities in Syria, this is an understandable reaction. But such criticism misunderstands the nature of the R2P.

The doctrine is ambitious, but also pragmatic and limited. It calls for military intervention only as a last resort, when the international community is united in its aims and when force stands a good chance of improving a situation. R2P has failed to prevent mass slaughter in Syria and all atrocities against civilians worldwide, but despite its limits, the concept that civilians have a right to protection has gained widespread support. This idea will not go away and R2P will likely be a powerful tool in future contexts, especially those in which regime change is not the goal of the international community.

Libya revealed both the promise and the constraints of R2P. In March 2011, after two months of fighting between government and rebel forces, the Libyan strongman Muammar al-Qaddafi issued an explicit threat to the residents of Benghazi, demanding that they suspend their rebellion. With Libyan forces moving toward the city, the UN Security Council invoked R2P and passed Resolution 1973, authorizing NATO to use force to protect the citizens of Benghazi. China and Russia refrained from vetoing the resolution, allowing the NATO-led military campaign to move forward.

NATO airstrikes stopped Qaddafi’s army in its tracks and helped prevent mass casualties in Benghazi. But Qaddafi still remained in power in Tripoli, and so the international forces faced a dilemma, one that is inherent to international intervention and civilian protection: how to intervene in a way that stops a government from killing its citizens and also establishes the necessary political, economic, and social conditions to enable the international community to suspend its actions without a resumption of violence. After the initial stages of the military campaign, the United States and NATO concluded that long-term stability required Qaddafi to step down. U.S. President Barack Obama and Secretary of State Hillary Clinton argued that Qaddafi’s belligerence posed an ongoing threat to citizens throughout the rest of Libya. Others on the UN Security Council, however, objected to the use of R2P to justify regime change.

Debates over the scope of the international community’s responsibility to protect civilians have always confronted proponents of humanitarian intervention. Initially proposed by the International Commission on Intervention and State Sovereignty in December 2001, R2P in its earliest drafts called for an ambitious approach to stopping mass atrocities by requiring states to intervene in cases of genocide and ethnic cleansing and to contribute to post-conflict reconstruction. Between 2001 and 2005, however, the document was substantially revised. In its final wording, articulated in the 2005 World Summit Outcome Document, all references to the responsibility to rebuild and explicit language regarding an obligation to intervene were cut. The compromise language states only that the international community is “prepared to take collective action . . . on a case-by-case basis” -- a watered-down phrasing that the political scientist Thomas Weiss called “R2P lite.”

Despite these changes, a number of countries, including China and Russia, remain concerned about the doctrine, fearing that even in its revised form, the West can use it to deceptively gain support for liberal interventions. UN Secretary-General Ban Ki-moon has tried to mitigate such concerns, making clear that the primary responsibility to protect civilians lies with the state they live in, and that the role of the international community should be to help governments develop this capacity. Military intervention should be considered only when all other options have been exhausted, when there is an imminent risk of mass atrocity, when backed by the Security Council, and when there are reasonable prospects of success and little likelihood of making the situation worse. Russia and China have balked at invoking R2P in Syria -- not because they support Bashar al-Assad's regime but because they worry that Washington wants to use the guise of humanitarian intervention to pursue a broader campaign of regime change worldwide. The United States’ demand that Assad step down has only hardened Moscow’s and Beijing’s opposition to taking action in Syria.

But even if Russia and China were on board, the situation in Syria differs from that in Libya in two important ways. First, the prospects for a successful military intervention in Syria are less promising than they were in Libya. According to the International Institute for Strategic Studies, as of 2009, Syria’s military was four times larger than Libya’s, with roughly 300,000 active duty troops and another 300,000 reserves. Syria also has an estimated 60,000 air defense troops and more than 4,500 anti-aircraft sites throughout the country -- many located in densely populated urban areas. Libya’s air defense command had far fewer troops and only approximately 300 anti-aircraft batteries. Moreover, the Syrian opposition has continually struggled to unify and to control territory. In Libya, by contrast, when the UN agreed to intervene, a unified opposition force controlled a large, contiguous portion of the country and it was clear that air support would help the rebels maintain their position.

Second, Qaddafi had little regional or global support, and the decision to intervene had the backing of all relevant international and regional organizations. With Syria, the international community remains divided. The Assad regime has a powerful ally nearby in Iran, and can count on Russia to block international pressure for regime change. In addition, the presence of Islamist militant fighters in the Syrian opposition is worrisome given the strength of al Qaeda in neighboring Iraq.

As events change on the ground, the international community may yet find some way for a limited intervention -- perhaps deploying anti-aircraft systems to establish a no-fly zone over northern Syria. The underlying complexities and challenges of intervention, however, remain. Even as there has been a dramatic rise in global cooperation to control and mitigate armed violence against civilians, state sovereignty and geopolitical realities still constrain these efforts.

To overcome these challenges, the United States and the international community need to decouple regime change from R2P. The doctrine will lose legitimacy if it is seen purely as an instrument of neoimperial adventurism. In an effort to prevent such misuse, Brazil, in 2011, introduced the concept of Responsibility While Protecting (RWP), which calls for increased UN Security Council monitoring and review of R2P actions. Brazil’s proposal was initially met with a tepid response by the United States, France, and the United Kingdom, who feared it would lead to slower international responses to mass atrocities. But the concept is now gaining support; Ban endorsed it in a July 2012 report. Mitigating concerns that R2P will be misused, RWP might help the international community strike the right balance between maintaining the support of the UN Security Council and effectively responding to mass atrocities in a timely manner.

In addition, the international community would do well to strengthen the nonmilitary elements of R2P. For example, countries should strengthen watchdog structures, such as the UN Office of the Special Adviser on the Prevention of Genocide, which coordinates the monitoring of serious human rights violations in conflict zones and issues early warnings reports to the Security Council. And when the prospect of military intervention is controversial, as is the case with Syria, the international community should still launch humanitarian and diplomatic initiatives as soon as there is evidence of impending mass killing of civilians. In Syria, the lengthy debate over intervention meant that other, nonmilitary tools, such as targeted humanitarian relief and coordinated diplomatic efforts, were not fully deployed to alleviate civilian suffering.

The international community is still figuring out how to prevent and manage violence against civilians. R2P has a mixed record, but that does not mean that it has failed. Taken together with other conflict prevention and management strategies, R2P and its core principle -- that civilians have a right to protection -- remain essential to continuing the trend toward a more peaceful world.