MASS MIGRATION, on the sustained and massive scale that western Europe continues to experience, creates tensions not only within states but also between them. These tensions will sometimes erupt into open conflict; already a new age of “Migration Wars” has begun.

This represents a curious inversion. Across the centuries, war has been a major, and often the main, driving force behind mass migration. Most obviously, an indeterminable number of civilians was forced to flee the fighting that raged in Europe and elsewhere during the Second World War, while the ongoing civil war in Syria has created perhaps 5.3 million refugees, in addition to many others who are “internally displaced.” Today, however, not only does war continue to cause mass migration, but it can itself become a cause of war.

This is the case because of the sheer scale of the current migrant crisis. The UNHCR estimates that there are around 65.6 million “forcibly displaced” people in the world. Most of these are internally displaced within their own countries, but around 22.5 million are refugees from their native lands. Huge numbers of people have fled from countries (“of departure”), notably Syria, to start new lives in the West, risking their lives by undertaking often extremely hazardous journeys across the Mediterranean or overland through countries (“of transit”) such as Turkey and Greece: in the first seven months of 2017 alone, 115,109 migrants succeeded in crossing the Mediterranean. And the total number of asylum applications to western Europe jumped considerably in 2014–15, from 0.6 million to 1.4 million, falling slightly to 1.3 million in 2016, while many other migrants, unquantifiable in number, have illicitly reached Western territory without formally requesting asylum.

Parts of the world besides western Europe are also affected: since August 2017, for example, around half a million Rohingya people have fled violence and persecution in their native Myanmar for the relative sanctuary of neighboring states, notably Bangladesh, Thailand, Indonesia and Malaysia. Above all, in sub-Saharan Africa millions are fleeing poverty from the landlocked states of the Sahel and heading for the relative prosperity of West Africa: around one fifth of Côte d’Ivoire’s population, for example, comprises people who were born elsewhere.

The sheer vastness of this contemporary refugee crisis does not represent any increase in the number of wars and conflicts, although it is arguable that, because of the proliferation of small arms in recent decades, this is one cause: in a speech in 2000, for example, UN secretary-general Kofi Annan warned that the bloodshed created by small arms and light weapons meant that “they could well be described as ‘weapons of mass destruction.’” But more important is the proliferation of economic migration, as increasing numbers flee poverty at home. The causes of this may be varied—some blame overpopulation, or the destructive impact of climate change upon food sources—but one driving force is the heightened awareness that many refugees have. Because of images broadcast on satellite television, mobile phones and the internet, they are aware, in a way earlier generations were not, of the relative material comfort the developed world can offer. This is probably the reason why some relatively affluent African countries, such as Senegal, also have high outflows of migrants.

Another difference lies in the proliferation of criminal gangs that, in return for exploitative fees, organize and finance their journeys. Such trafficking gangs are prevalent in two major hubs of migrant movement: Thailand, which is a transit point for Rohingya refugees, and Libya.

Whatever the causes, this major movement of people has now acquired its own momentum. Because so many refugees have reached the shores and borders of, in particular, western Europe, and because so much media attention has focused on this new phenomenon, an idea has taken hold in the minds of many people who would never otherwise have contemplated undertaking the hazardous crossing of the Mediterranean Sea or overland journey through Central Asia or the Balkans: that it is possible to start a new life in distant but affluent countries. This has been accentuated by the decision of the German government, taken in 2015, to open its borders to around one million refugees. In other words, many of the millions who have fled to Europe in the past few years have climbed on a bandwagon, following what they have seen others do rather than what they have been forced, by adverse circumstance, to undertake. Despite the determined efforts of Western governments to stop them, there is no reason they will not continue trying to do so.

SUCH A vast migrant flow, or even its mere threat, will tempt Western governments to intervene in foreign lands—either countries of departure or transit countries, such as Libya—in a bid to curb those flows. This, of course, is nothing new. One country always has an interest and motive to intervene in the affairs of another if it is being affected by a flow of refugees from that country; this was true, to take one obvious example, of Western involvement in the Balkan Wars of the early- to mid-1990s. But the advent of sustained mass migration, from so many different venues and across so many different routes and borders, is a new phenomenon that is prompting changes of strategic direction in Western capitals.

Such “migration interventionism” could of course be entirely peaceful—such as the provision of foreign aid, for example, to specific programs and initiatives that are designed to reduce the level of migration. But it could also take more ambitious, militaristic forms, such as troop deployments to stabilize foreign countries, or regions within them, that are experiencing, or could potentially experience, a significant outflow of population. This would not only reduce or eliminate any incentive for putative migrants to leave, but also allow those foreign governments to deport and return existing migrants to a “safe country”: many international and domestic laws (Article 16a of German Basic Law is an example) prohibit the deportation of a refugee to a country that is not “safe.” However, the legal and practical difficulties of deporting migrants may mean that “migration interventionism” will, in the years ahead, be undertaken more as a preventive exercise—to prevent any possible outflow—than a reactive one.

The emergence of migration interventionism became clear at the Munich Security Conference in February 2017, when the UK defense secretary, Sir Michael Fallon, justified the ongoing, if limited, British presence in Afghanistan on the grounds that the collapse of the country would lead to a massive refugee crisis. “We here will feel the consequences, very directly,” he claimed. “There could be three to four million young Afghan men sent out by their villages to migrate westwards, and they are heading here.” This was a new justification for the allied presence in Afghanistan, which had previously been rationalized on a number of other grounds, varying from combating terrorists who presented a threat to the West to preventing the flow of narcotics and establishing democracy and human rights.

It is possible that any future Chinese military intervention in North Korea, in a bid to resolve the ongoing deadlock surrounding Kim Jong-un’s nuclear provocation, could also become a kind of migration interventionism. Any conflict between North Korea and the United States, or perhaps merely heightened risk of such a conflict, would provoke a huge exodus of North Korean refugees over the northern border, overwhelming Chinese resources.

Instead of committing their own troops overseas in order to prevent or reduce migration into their territory, governments can also sponsor foreign armies to act on their behalf. An example is the G5 Sahel Joint Force, which the French government, supported by other Western countries, began to establish in the Sahel in the course of 2017. Comprising five thousand soldiers drawn from the armies of Burkina Faso, Mali, Mauritania, Niger and Chad, the force is funded by the EU, whose leaders regard it partly as an anti-insurgent force, but also as a means of reducing the flow of migrants. “Our support will be an important contribution to the efforts to counter terrorism in the Sahel region, as well as irregular migration from West Africa to Europe,” the Danish minister for foreign affairs, Anders Samuelsen, has said. The force is also sanctioned by UN Security Council Resolution 2359, which points to the “serious challenges posed by . . . the smuggling of migrants [and] trafficking in persons” from the Sahel. In the future, such a force could also guard any Western nationals who are posted on foreign soil in order to process asylum claims. (It was just such a proposal that the French president, Emmanuel Macron, appeared to make in the summer of 2017 when he said France could establish processing “hotspots” in Libya—which, since the overthrow of Muammar el-Qaddafi in 2011, has been a major departure point for millions of refugees.)

Countries that are seeking to stem the migrant flow into their own territory are also increasingly diverting their existing military resources, not just within departure states, but also outside their borders. In the summer of 2015, for example, the EU began EUNAVFOR MED, a naval operation in the Mediterranean Sea that was intended to end human smuggling from Libya by seizing or destroying some of the boats that the gangs were using. Under its mandate, this €12 million operation involved “boarding, searching, seizing and diverting” smugglers’ boats, and wherever possible, efforts to “dispose” of those vessels. “This important transition,” as an EU official argued, “will enable the EU naval operation against human smugglers and traffickers in the Mediterranean to conduct boarding, search, seizure and diversion on the high seas of vessels suspected of being used for human smuggling or trafficking, within international law.” Vessels, drones and aircraft drawn from at least ten member states formed part of what the EU’s foreign-policy chief, Federica Mogherini, called a “holistic” approach to the migrant crisis.