At first glance, the U.S. decision to escalate the war in Vietnam in the mid-1960s, China's position on North Korea's nuclear program in the late 1990s and early 2000s, and the EU resolution to lift what remained of the arms embargo against Libya in the mid-2000s would appear to share little in common. Yet each of these seemingly unconnected and far-reaching foreign policy decisions resulted at least in part from the exercise of a unique kind of coercion, one predicated on the intentional creation, manipulation, and exploitation of real or threatened mass population movements.

In Weapons of Mass Migration, Kelly M. Greenhill offers the first systematic examination of this widely deployed but largely unrecognized instrument of state influence. She shows both how often this unorthodox brand of coercion has been attempted (more than fifty times in the last half century) and how successful it has been (well over half the time). She also tackles the questions of who employs this policy tool, to what ends, and how and why it ever works. Coercers aim to affect target states' behavior by exploiting the existence of competing political interests and groups, Greenhill argues, and by manipulating the costs or risks imposed on target state populations.

This "coercion by punishment" strategy can be effected in two ways: the first relies on straightforward threats to overwhelm a target's capacity to accommodate a refugee or migrant influx; the second, on a kind of norms-enhanced political blackmail that exploits the existence of legal and normative commitments to those fleeing violence, persecution, or privation. The theory is further illustrated and tested in a variety of case studies from Europe, East Asia, and North America. To help potential targets better respond to—and protect themselves against—this kind of unconventional predation, Weapons of Mass Migration also offers practicable policy recommendations for scholars, government officials, and anyone concerned about the true victims of this kind of coercion—the displaced themselves.

Praise for Weapons of Mass Migration:

"Kelly M. Greenhill's Weapons of Mass Migration shines a bright light on strategically engineered migration. And this is, unfortunately, no minor issue. The reader is astounded by how many times states have engaged in such violent action. Greenhill gives the subject the attention it deserves, skillfully unpacks why some states engage in forced migration while others do not, discovers interesting theoretical twists, and derives tractable policy recommendations."—Michael Barnett, Harold Stassen Chair at the Hubert H. Humphrey School, University of Minnesota

"Kelly M. Greenhill's fine analysis gives a double meaning to the notion of weapons of the weak: tin-pot dictators try to get bargaining leverage over neighboring democracies by threatening to swamp them with refugees. This has happened on average once a year over the past half century. Those interested in refugees or in creative bargaining tactics will be fascinated by this tale."—Jack Snyder, Robert and Renée Belfer Professor of International Relations, Columbia University

"Weapons of Mass Migration is a truly valuable contribution. This incisive book highlights an unconventional and nonmilitary method of state-to-state coercion—why and how weak states increasingly deploy the threat or reality of 'strategic engineered migration' to achieve political goals that would otherwise be unattainable. The book argues convincingly that this underappreciated form of interstate 'political blackmail' is both more frequent and more effective than commonly supposed. Its most likely targets are liberal democracies whose human rights commitments and diverse political interest groups can be exploited to impose what the author terms 'hypocrisy costs' upon any government that resists such coerced outmigration. Yet even authoritarian states such as modern China are vulnerable, as the North Koreans have shown. This book unveils an effective weapon of asymmetric statecraft that has been 'hiding in plain sight.' It deserves attention from all those interested in emerging patterns of international relations and human rights."—Michael S. Teitelbaum, Alfred P. Sloan Foundation and Harvard Law School