Such operations raise the prospect of confrontation and military clashes between recipient states and countries of departure and transit. When the Italian government sent two patrol ships close to the Libyan coast in August 2017, for example, Gen. Khalifa Haftar, the ruler of a large swath of Libya, threatened to attack them if they entered Libyan waters to search and destroy refugee boats: “Commander-in-Chief of the armed forces, Field Marshal Khalifa Haftar, issues orders to the Libyan naval bases in Tobruk, Benghazi, Ras Lanuf and Tripoli to confront any marine unit that enters the Libyan waters without the permission of the army,” a statement from the Libyan National Army proclaimed. His warning reflected a growing popular anger among Libyans against Italian interference in their domestic affairs.

Such clashes may be more likely if a foreign government threatens to exploit or manipulate a refugee crisis in a bid to extort concessions from other countries toward which those migrants are likely to head. This appears to have been true of the Libyan government under the rule of Qaddafi. Addressing a gathering in Rome in August 2010, Qaddafi had claimed that unless he was given large sums of money, Europe would experience the “advance of millions of immigrants” that would transform it into “another Africa.” He had added that “tomorrow Europe might no longer be European and even black as there are millions who want to come in,” and alleged that “we don’t know if Europe will remain an advanced and united continent or if it will be destroyed, as happened with the barbarian invasions.” Demanding a payment of €5 billion to prevent this from happening, his comments were condemned as “unacceptable blackmail” by Italian parliamentarians. In the context of these remarks, it is possible that the Anglo-French attack on Libya in 2011 was the first migration war of the contemporary age: this may explain why, from the onset of the crisis, in March 2011, the French president, Nicolas Sarkozy, and the British leader, David Cameron, sought to oust Qaddafi from power and ignored his offers of peace talks.

Turkey, which is the host of over three million refugees, has made similar sallies at political blackmail in recent years against the European Union: in March 2017, Turkey’s President Recep Tayyip Erdoğan threatened to tear up a key migrant deal with the EU, in apparent retaliation for a ban placed by the German and Dutch governments on political rallies by his followers living in those countries. Istanbul had already struck a hard bargain when negotiating the deal, which came into effect in March 2016, having demanded in return a $3.3 billion aid package and new negotiations on its membership in the European Union. Should other states use similar tactics against more powerful ones in the future, they may risk provoking armed attack.

BESIDES FOREIGN intervention in countries of departure, or armed clashes with governments that seek to manipulate migration, the world will witness other types of migration wars. In particular, foreign powers may deliberately create, or exacerbate, a refugee crisis in another country in order to divert the resources of the countries where those refugees are likely to go. Of course, innocent civilians have always been deliberately targeted in times of war: during World War Two, the Allied bombing campaign was designed to undermine German civilians’ morale and shorten the war. However, deliberate attempts to drive civilians out of a country, in a bid to weaken a third party, have historically been much less common. Such a scenario is more likely to happen today for the simple reason that a sustained mass migration of people is already under way. This means that a government or militia has more opportunities to manipulate the phenomenon, because it is easier to accentuate any such movement than to create one; it is also less likely to risk international condemnation by observers who cannot so easily blame foreign intervention.

An example is the post-2011 Syrian refugee crisis. In March 2016, several months after Russia had openly intervened in the conflict on the side of President Bashar al-Assad, Gen. Philip Breedlove—the Supreme Allied Commander Europe and head of U.S. European Command—claimed that Vladimir Putin and Assad had “weaponized” migration through a campaign of bombardment against civilian centers. Their agenda, he continued, was to undermine NATO and western Europe: “Together, Russia and the Assad regime are deliberately weaponizing migration in an attempt to overwhelm European structures and break European resolve,” General Breedlove told the Senate Armed Services Committee. In particular, Russia’s indiscriminate use of weapons, such as barrel bombs, seemed to have “no other purpose” other than to get civilians “on the road.”

It is also likely that the Islamic State (ISIS) has deliberately created or accentuated the flow of refugees from Iraq and Syria. Its shocking acts of cruelty, such as the beheading of captives, and the careful propagation of such images on the Internet, had a clear rationale: to strike fear into the hearts of civilians and force them to flee. Its advances during 2014–16 led to the displacement of three million in Iraq, with far more internally displaced—more than 1.5 million in the Kurdish region alone.

ISIS calculated that this would not only clear a path for its own foot soldiers, but also overwhelm the resources of neighboring and perhaps pro-Western regimes, such as Lebanon and Jordan, while adding to the flow of refugees into western Europe. In the long term, this would probably be seen as a way of “Islamizing” the West—increasing the numerical presence of Muslims—but most obviously, in the short and medium terms, it was a means of infiltrating Europe with sympathizers: there have been numerous attacks across Europe, including Paris, Nice, Manchester, London and Berlin, by ISIS-linked insurgents. And in December 2016, Europol published a report that pointed out another danger: “A real and imminent danger is the possibility of elements of the [Sunni Muslim] Syrian refugee diaspora becoming vulnerable to radicalization once in Europe and being specifically targeted by Islamic extremist recruiters,” argued the authors of “Changes in Modus Operandi of Islamic State Revisited.”

However, it is also possible that Islamic State had another motive. Instead of deliberately creating a flow of refugees in order to carry out attacks or overwhelm its enemies’ resources, it may have been trying to provoke them to undertake a “migration intervention.” Its motive for doing this would have been either to spark a confrontation with other regional actors or to tie down foreign troops in a protracted insurgency and steadily drain its resources. For example, if NATO had undertaken a large-scale deployment into parts of Syria to fight ISIS, then its presence would have sparked a conflict not just with President Assad but also with his chief supporter, Russia. Alternatively, NATO troops would have faced sustained casualties from a protracted insurgency, comparable to the conflict that they (and the Russians) fought in Afghanistan as well as the experiences of the United States in Vietnam in the 1960s, and Israel in Lebanon in the 1990s.

THE ADVENT of sustained mass migration could also trigger conflict if a country tried to forcibly return or expel some or all of its new arrivals. This scenario is, of course, also a recipe for civil unrest. The migrants themselves may resist: such violence broke out at Calais in northern France in the fall of 2016, for example, when the French riot police forcibly removed thousands of refugees from a camp known as “The Jungle.” However, violence could also break out between neighboring states, for instance if one tried to drive refugees away from its own territory onto the soil of the other; or if it closed its own border to stop a column of refugees crossing its own borders, thereby forcing them to move into, or remain within, another country.

This scenario is already causing political conflict within the EU, as the Polish and Hungarian governments continue to resist demands for a quota of refugees that other member states, notably Italy, Germany and France, are already hosting. However, it could in some circumstances spark military confrontation—for example, between countries that already have unstable and tense relations, or even when countries of destination are severely overstretched by the strains of coping with a large influx of people. This nearly happened in Southeast Asia in the late 1980s, when a huge exodus of civilians from Vietnam, Laos and Cambodia threatened to overwhelm neighboring countries—Hong Kong, Malaysia, Thailand, the Philippines and Indonesia—which, in return, used naval and police boats and helicopters to push back refugees away from their coasts. The prime minister of Malaysia, Mahathir Mohamad, admitted, “All we are doing is preventing foreign vessels from entering our waters.”

Another variety of migration wars will break out when migrants from one country will be pursued and persecuted by militias—or perhaps by government forces—based in their countries of origin. This may be because, for example, those soldiers seek to take revenge, or to destroy a political cause that the refugees are seen to represent. Such cross-border attacks would then trigger conflict with the host country in which those migrants have taken refuge. Such a scenario took place in Zaire (now the Democratic Republic of Congo) in the mid-1990s, as Rwandan troops crossed the border, killing thousands of Hutu refugees who had fled there. This provoked resistance from the Zairean army, whose leader was broadly sympathetic to the Hutu cause. More recently, in September 2017, there were also reports that Myanmar helicopters had crossed into Bangladeshi airspace in hot pursuit of Rohingya refugees.