This problem is being felt far from the battlefield. Following the precedent set by Al Qaeda, which nurtured relations with like-minded groups and eventually made them formal affiliates, the Islamic State has used the conflict to grow in power and declare “provinces” in the Sinai, Libya, Saudi Arabia and Yemen, among other areas. The meaning of this affiliation is mostly unclear, and so far the Islamic State “provinces” have not dramatically altered the courses of local civil wars (or, in the case of Nigeria, Boko Haram’s assumption of the Islamic State mantle has not changed the group substantially). However, in Libya, the Islamic State has deployed money and foreign fighters to help its local allies advance, enabling them to carve out small parts of the country and put them under Islamic State control.

 

CIVIL WARS also lead to the radicalization of politics in neighboring states. Refugees bring politics with them: the Palestinian cause was at the center of intra-Arab maneuvering for decades, and its turbulence led to coups and civil strife in many Arab countries. Similarly, terrorism, another effect of spillover, can destabilize neighboring state politics, weaken governments and allow regimes to exploit the violence to discredit their enemies. Some governments may step up repression to stop potential unrest, exacerbating concerns about discrimination. Finally, violence often highlights grievances or problems in another country, raising awareness and demands for better treatment.

Civil wars also create new issues that upset delicate equilibria in local politics. In Iraq, Jordan and Lebanon, large refugee flows are altering fragile demographic balances, leading some communities to oppose the refugee presence for fear that refugees will aid their local enemies. The civil war in Afghanistan spilled over into Pakistan, with groups like the Pakistani Taliban terrorizing Pakistan itself and poisoning relations between Shia and Sunni there. The spread of radical ideas from one country to another is particularly likely in conflicts like that in Syria, where the people living across the borders enjoy family, linguistic, ethnic, religious and historic ties with Syrians. Alevis in Turkey have ties to Alawis in Syria; Syria’s Kurds have ties to Kurdish communities in Iraq and Turkey; and of course the Shia and Sunni populations of Iraq and Syria have sympathetic communities in neighboring states. These communities often demand their own governments intervene, and they often privately mobilize to provide their own assistance or gain government blessing and support to do so. In Lebanon and Iraq, the people are also split communally, and the government’s actions (or inactions) in Syria are yet another source of grievance. This radicalization was particularly visible in Iraq, where even before the Islamic State advanced there in 2014, the sectarian violence in Syria strained relations between the Sunni and Shia communities. In Saudi Arabia, too, sectarian rhetoric and anti-Shia violence are fueling tension between the kingdom’s Sunni majority and Shia minority.

 

ALL THESE pressures can contribute to regional intervention. Academic research indicates that the presence of civil wars increase the likelihood of conflict between states as neighboring regimes seek to shape the civil war’s outcome and manage its spillover effects. Pakistan sent its own military and intelligence officers to bolster the Taliban in the 1990s; Kenya intervened in Somalia to help push back Al Shabab; Rwanda, Uganda and other neighbors intervened in Congo to back favorites; and so on: the combination of perceived threat and opportunity has at times proved irresistible. The United States, too, sometimes intervenes when small civil wars became big ones.

In Syria, Iran intervened early in the civil war to prop up Assad, and its assistance may have been decisive in allowing the Syrian regime to survive the war’s initial years. Jordan and Turkey assist antiregime rebels, with Jordan shifting support from the Free Syrian Army to Syrian tribes, while the Iraqi government, somewhat more slyly, facilitates Iranian intervention on its territory. The Assad regime, weak and focused on holding on at home, has largely refrained from retaliating against neighbors supporting rebels, but it was reportedly behind a 2013 bombing in a Turkish border town that killed more than fifty people, mostly Turkish citizens. Turkey has joined the U.S.-led intervention against the Islamic State—but it directs the bulk of its military efforts against anti-Turkish Kurdish rebels who have based themselves in Iraq. The heightened sectarian environment and the growing Iranian-Saudi rivalry in Syria and Iraq have also led both countries to step up intervention in Yemen, which each sees as yet another front in the broader war. Substate groups like Hezbollah in Lebanon or Sunni tribes in Iraq also work with their favorites across the border. Intervention tends to produce a spiral, with intervention increasingly occurring because others are intervening.

 

SPILLOVER CANNOT be stopped completely, but it can be contained to minimize its effects. The goal of containment is to prevent the strife from spreading further and to stop outsiders from worsening the violence within Iraq and Syria, thereby making it at least somewhat more likely to peter out on its own. In practice, containment would involve several measures, each linked to a different dimension of spillover.

First, the refugees demand care—both because of the strategic risk they pose and because of the moral imperatives. Since the Syrian crisis broke out, the United States has provided billions of dollars of humanitarian aid, with much of that going to refugees or those within Syria. Outside of aid to those displaced inside Syria itself, Lebanon and Jordan are the largest recipients, and the United States is increasing aid to Jordan and providing loans for economic support. Europe has given comparable amounts to Syria’s neighbors and taken in many thousands of refugees.

This aid is significant, but a larger-scale effort is necessary to care for the refugees. Neighboring countries, especially the poorer ones like Jordan and Lebanon, need additional financial support to care for refugees in camps and to integrate them into society when possible. In Lebanon refugees have often settled into the country’s poorest neighborhoods, and their presence has exacerbated tension between Sunnis and Alawis in cities like Tripoli. Other states should help with the burden. When Hungary briefly stopped the transit of refugees in September 2015 and high-profile migrant deaths occurred elsewhere in Europe, it prompted broader soul-searching across the continent with Austria, Germany, and other countries vowing to take in significantly more refugees—an important step in the right direction. The United States plans to take in more Syrian refugees than before, but this number could still be increased further. More support for refugees allows the United States, for a fraction of the cost of significant military intervention, to offset some of the humanitarian horror of the war and reduce the risk of spillover from refugee flows.

 

HOST-COUNTRY efforts to police refugee camps also need international support. The large population of the camps necessitates large security forces to police them. In addition, intelligence assistance at times will be necessary to ensure that host governments are aware of potential militants and able to disrupt their activities.

In addition to caring for refugees, an effort should be made to resettle them far from the borders of the conflict zone and integrate them into their host societies, thus making them both less willing and less able to join or support militant groups back in their home countries. This will require host countries to accept that the refugees are likely to stay for the long term, a financially costly and politically contentious issue for them. The long-term cost of a failure to integrate is high. Marginalized refugees will not contribute to their host economies and may be a source of radicalism. In Jordan, half the population is officially refugees from the age-old Palestinian diaspora, the latest influx of Syrians, or the previous round of Iraq wars. In Lebanon, refugees make up a fifth or so of the total population. In these countries, complete integration of even more refugees is unrealistic. Other countries, including the United States, must share more of the burden.

 

IMPROVING BORDER security is vital. In 2015, Jordan’s border guards may receive over $10 million in U.S. funding. This is a valuable first step, but further emphasis on the border guards and others who may be the first line in stopping Islamic State incursions and managing refugee flows is vital for U.S. allies. Turkey has also moved slowly to prevent the passage of volunteers to the Islamic State and resisted U.S. and European pressure to step up efforts, often claiming it cannot secure its long border with Syria. The primary problem is political, not one of capacity, but Washington should make a show of helping Turkey on the capacity side with technological aid as a way of gaining Ankara’s goodwill and allowing it a face-saving way to explain its past laxity.

Neighboring countries will also need significant counterterrorism assistance, both to monitor and police the refugee camps and to prevent groups like the Islamic State from launching attacks. Money will talk, as the security services will need additional resources to meet the additional threat. The United States in 2015 provided roughly $1 billion in overt security aid to Jordan, and this figure may need to be increased. Some will also need more robust training programs, though several, notably those in Jordan and Saudi Arabia, are strong already. America’s own extensive intelligence efforts, particularly in high-tech fields like signals intelligence, will be valuable and should be shared with U.S. allies. The United States will also have to help coordinate intelligence efforts. The Islamic State and other groups are diffuse targets, and Washington needs to make sure that information gathered by one country is shared with relevant officials in others—a difficult task given the mutual suspicions that plague the neighborhood.