Editor's Note: As the U.S. military draws down in Afghanistan, the large-scale conventional military component of the “war on terror” may be at an end. Yet Al Qaeda is tied to many of the insurgencies currently raging in countries around the world, and more broadly, sub-state conflicts continue to pose a threat to international peace and security. To confront these insurgencies, U.S. policymakers need a range of options for intervention, whether such intervention is undertaken in the name of counterterrorism, humanitarian concerns, or other U.S. goals. One option that is often touted as a particularly effective and economical approach is the use of “small-footprint” deployments—that is, sending limited numbers of special operations forces, advisors, and other personnel to assist foreign allies and their militaries in the fight against shared enemies. Stephen Watts, a senior political scientist at RAND, contends that such interventions demand a closer look: their success rate is often poor, and human rights abuses and other problems are common.

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The United States is deeply concerned about the potential for countries like Libya, Mali, Somalia, Syria, Yemen, and others to export insecurity—particularly terrorism, but also other forms of violence and instability. However, Washington is not willing to dedicate substantial resources to dealing with these crises, as it did in the counterinsurgencies of the 2000s or the peace operations of the 1990s. As President Obama’s 2012 Defense Strategic Guidance proclaims, the United States “will develop innovative, low-cost, and small-footprint approaches to achieve our security objectives.”

If this policy sounds familiar, it should. It is not the first time the United States has adopted such an approach.

Facing a country exhausted by years of fighting in Vietnam, President Nixon in 1969 declared a core principle of what would become known as the Nixon Doctrine: “We shall furnish military and economic assistance when requested...But we shall look to the nation directly threatened to assume the primary responsibility of providing the manpower for its defense.” This announcement would pave the way to the “Vietnamization” of the war in Indochina—and also to U.S. participation in proxy conflicts throughout the developing world. These wars limited the expansion of Soviet influence at an extremely low cost in terms of the number of American soldiers deployed abroad. They also led to an enormous spike in the number of wars and war-related deaths around the globe. Most of these wars ultimately only ended (if they ended at all) with the end of the Cold War, not as a result of the victory of America’s proxies.

The history of “small-footprint approaches” should be sobering. It suggests that such approaches are good at preventing allied governments from losing against rebels, but are not very good at actually winning wars. Meanwhile, the costs of conflict—including spillover effects such as refugee flows, illicit trafficking, and transnational terrorism—continue to accrue.

Proponents of such interventions—which include a large number of thinkers in the U.S. defense community—typically point to recent U.S. successes in the Philippines and Colombia, where small contingents of U.S. forces have helped partner governments turn the tide of their counterinsurgency campaigns. Unfortunately, these proponents seldom ask whether these successes are replicable elsewhere.

To answer that question, a team of researchers I led at RAND examined the outcomes of 72 cases of insurgency that have ended in the post-Cold War era, as well as more in-depth case studies of the Philippines and Pakistan. The study found that so-called success stories like the Philippines and Colombia all occurred in countries with relatively inclusive politics and reasonable levels of state capacity. In such countries, governments typically adopt strategies approximating the “hearts and minds” approach. But only about one insurgency in eight occurs in such best-case conditions. Most rebellions take place in worst-case environments—in countries that lack both inclusive politics and state capacity. In such cases, governments tend to rely on blunt military force to contain or suppress rebellion.

These differing environments dramatically shape the prospects for success. Only 13 percent of civil wars in the best-case environments fail to reach an outcome acceptable to the government (either outright military victory or a peace deal acceptable to both the government and the insurgents). The failure rate in worst-case environments is 60 percent—approximately five times worse than in the sorts of countries that have been touted as “success stories” of small-scale intervention. This is not to downplay the importance of U.S. assistance in Colombia and the Philippines; clearly it played a critical role in these conflicts. But it is a mistake to generalize from U.S. experiences in these countries and assume that similar small-footprint approaches will work elsewhere.

What should policy makers do with this information? First, it should serve as a warning against relying on small-footprint approaches in countries where the governments are weak and rely on a narrow base of support. Not only are the odds stacked against success in such cases, but these governments are much more likely to commit mass killings as part of their counterinsurgency campaigns—according to our research, approximately four times as likely. With U.S. public attention monopolized by the wars in Iraq and Afghanistan, U.S. security assistance in other parts of the world generally has not had to face a great deal of scrutiny in recent years. That is likely to change in the future. Abuses by partner-nation forces can have strategic consequences for donors, as the United States learned in El Salvador and France learned in Rwanda (to cite only two cases among many). Ideally, the U.S. Department of Defense would adopt a much stronger, more systematic process of screening potential recipients of U.S. military assistance, using quantitative and qualitative metrics to identify areas of particular risk and undertaking strategies to avoid or mitigate such risk.

Second, the United States should understand the limits of its leverage. Classics of the counterinsurgency literature and more recent quantitative analyses of development assistance agree: conditionality is extremely limited in what it can accomplish when the partner nation is of strategic importance to the donor. The United States can use conditionality to push partner nations to reform at the margins, and it can and should establish “red lines” which, if violated, would cause the United States to withdraw its assistance. In Sierra Leone, for instance, the United Kingdom was able to exercise leverage effectively when the incumbent Sierra Leone People’s Party (SLPP) threatened to abrogate the results of the opposition’s victory in the 2007 elections. However, this successful enforcement of one of the U.K.’s red lines was possible in large part because Freetown was highly dependent on British aid, and because the U.K. had no strategic interests in Sierra Leone, thus making its threat to withdraw assistance more credible. Beyond these limited uses, though, conditionality is unlikely to accomplish very much.

Third, the United States can facilitate conflict termination and mitigate the risks of partner abuses in the conduct of counterinsurgency. It can help partner regimes credibly commit to political compromises with reconcilable elements of the armed opposition through a variety of instruments, potentially including large-scale commitments of foreign aid and, in some contexts, international peace operations. And it can emphasize civilian oversight, inclusive personnel policies, and other accountability mechanisms in its security sector assistance—particularly in “Phase 0,” before a conflict begins.

Military interventions and foreign military assistance are not preordained to failure, but neither are they “fixable” through some clever new paradigm shift. They are a game of odds, and the United States can improve its odds at the margins through appropriate policies. Sometimes such policies can secure important gains at reasonable costs—as the examples of Colombia and the Philippines suggest. But the risks will inevitably remain high. Relying on small-footprint operations will not change this basic fact.

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Stephen Watts is a senior political scientist at the nonprofit, nonpartisan RAND Corporation. His research has focused on insurgency and counterinsurgency, stability and peace operations, security assistance, coalition diplomacy, and political development in the wake of civil wars. He formerly held fellowships at Harvard University’s Belfer Center and the Brookings Institution and served in the U.S. State Department.