In general, the United States should use arms sales and other forms of influence to reassure allies and gain influence over their decisions. At times these systems do little for counterterrorism or other shared threats: funding to Jordan, for example, helps its air force purchase advanced air-to-air missiles that do little to help Jordan against any of its current challengers. Still, systems that require U.S. assistance for logistics are valuable, as they give the United States a de facto veto over the use of these weapons and often the sustainability of a broader intervention.

IF CONTAINMENT works, it would prevent the conflagration that is consuming Iraq and has consumed Syria from inflaming violence in neighboring states and make neighbors less likely to escalate their involvement in Iraq. Indeed, it is possible that countries like Saudi Arabia and Iran might become less involved than they are now if they recognize that the fighting in Iraq is less likely to affect their interests directly. Containment also has humanitarian benefits: though it may seem callous to let existing fires burn, successful containment means the conflicts will be less bloody and less likely to spread. Refugees also will receive better care. Finally, successful containment will help manage the terrorism threat.

Containment is also far less costly than more aggressive options like direct intervention or partition. Containment does not demand a large-scale military presence, and even a significant aid package is far cheaper than deploying military forces. Diplomatically it is also less burdensome, though it would involve constant efforts to reassure and cajole allies and pressure adversaries.

Yet despite its considerable potential, many of the benefits of containment will be difficult to achieve. All of the governments in the region are skeptical of the U.S. commitment to their security. The United States and Saudi Arabia are at odds over the Iran nuclear deal, as well as over what Riyadh sees as U.S. vacillation in Syria and the abandonment of long-standing allies during the Arab Spring. The Obama administration’s desire to reduce the U.S. role in the Middle East has led other countries to share the Saudis’ skepticism. U.S. efforts to coordinate allied activity and to shape Iranian behavior are particularly unlikely to succeed.

Containment, moreover, means playing defense—it doesn’t solve any of the current problems, even if it stops some new ones from arising. The tremendous suffering of the civil wars will not end. The war may burn out on its own, but the United States would have little influence over who is the victor, and the possibilities include jihadists or the Assad regime, as well as the less loathsome but not particularly pleasant assortment of thuggish leaders usually found in the Middle East. In addition, the regional and local pressure waves the civil wars generate are often stronger than what the United States can do in response.

Both before and after the U.S. troop withdrawal from Iraq, Washington tried to use its diplomatic and moral power to convince the Iraqi government to be more inclusive and to ensure that the Iraqi military remained effective: both failed disastrously, and that was before the resumption of civil war raised the stakes even higher and made the cost of this failure more dear. Because it is difficult for containment to work, its low cost may be illusory, and indeed it may mean the problem metastasizes and the United States ends up paying a higher cost should it decide to take more aggressive steps in the future.

Yet in the end, containment is a necessity if the United States does not want to increase the scope and scale of its intervention. Accepting this, and acting accordingly, will check the damage to American interests.

Daniel Byman is a professor at the School of Foreign Service at Georgetown University and a senior fellow at the Center for Middle East Policy at the Brookings Institution. His latest book is Al Qaeda, the Islamic State, and the Global Jihadist Movement: What Everyone Needs to Know (Oxford, 2015). He tweets at @dbyman.

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