By Emily Tran
Kelly M. Greenhill is an Associate Professor of Political Science at the Tisch College of Civic Life at Tufts University, Director of the MIT-Seminar XXI Program, and a research fellow at the Harvard Kennedy School of Government Belfer Center for Science and International Affairs.
In her book Weapons of Mass Migration: Forced Displacement, Coercion, and Foreign Policy, Greenhill delivers a groundbreaking and unsettling study of how human movement can be weaponized in international politics. Drawing on over five decades of case studies and quantitative data, Greenhill argues that mass migration, often portrayed as a humanitarian crisis, can also serve as a deliberate instrument of statecraft, in what she terms “coercive engineered migration.” Her model of two-level asymmetric coercion shows how challengers, states, or non-state actors seeking to influence another government can pressure target states not through military force, but by imposing domestic social and political costs.
Greenhill sharpens this two-level asymmetric coercion framework into two interlocking strategies: swamping, which overwhelms a target’s capacity to absorb migrants, and agitating, which exploits domestic divisions and normative commitments to undermine its willingness to absorb migrants.
Methodologically, Greenhill balances large-N analysis, her broad quantitative examination of many coercive migration cases, with close comparison, using detailed case studies to capture the political dynamics. Between 1951 and 2006, she identified at least 56 cases of coercive migration, nearly three-quarters of which achieved at least partial success, meaning the target state complied with some of the challenger’s demands by changing a policy, reversing an action, or offering concessions.
Her case studies illustrate the theory’s wide range of application: Chapter 2 reconstructs three Cuban episodes, showing how the United States’ early refusal to negotiate with Castro magnified later costs. Chapter 3 examines Kosovo and NATO in 1999, where a generator (Milosevic’s failed gambit), an agent provocateur (the Kosovo Liberation Army), and an opportunist (neighboring Macedonia) each tested alliance cohesion by manipulating refugee flows. Chapter 4 argues that the 1991 to 1994 Haitian boatpeople crisis reveals how migration-driven coercion, orchestrated by exiled President Aristide of Haiti, forced the Clinton administration into a reluctant military intervention to restore Haiti’s democracy. Chapter 5 shows that in the 1990s to early 2000s, fears of a North Korean refugee surge bound migration and nuclear politics: China propped Pyongyang to avert collapse, while international activists and NGOs staged high-visibility events like filmed escape attempts of asylum seekers to pressure China through global media, which grew North Korea’s bargaining power. Across these chapters, the pattern holds: coercion succeeds when challengers tie cross-border movement to pre-existing domestic fractures.
Philosophically, the book examines how states instrumentalize people as bargaining tools and how migrant cooperation or resistance shapes those dynamics. When displaced populations align with provocateurs, coercion becomes more potent; when migrants pursue independent goals – departing in greater numbers, choosing new routes, or refusing to perform expected roles – coercion can fail. Greenhill never loses sight of this agency: migrants are not passive objects but active participants who can strengthen or unravel coercive designs.
One of Greenhill’s most insightful concepts is “hypocrisy costs,” the reputational penalties incurred when liberal democracies violate their own humanitarian ideals. Inverting the logic of “audience costs,” she argues that moral rhetoric can backfire: the higher a leader’s ethical claims, the greater the pressure to concede when those claims are tested. Greenhill stated in an interview, “In the current political environment, hypocrisy costs are playing a substantially diminished role in many cases, given the willingness of many potential target states to ignore, eschew, or sidestep their traditional obligations. Unfortunately, though, coercers have just placed greater reliance on other levers of influence.”
Perhaps Greenhill’s most unnerving claim concerns the unintended consequences of humanitarian norms: as post-1970s rights commitments and NGO activism grew, they inadvertently gave weaker actors leverage to exploit liberal states’ own values. This dynamic produces what she terms a “normative blowback effect,” in which the very norms designed to protect the vulnerable increase the attractiveness and efficacy of “coercive engineered migration” against democracies, prompting some targets to tighten asylum and immigration policies in response.
Ultimately, Greenhill shows that liberal democracies face an ethical paradox: the very norms that define them, transparency, compassion, and legality, can become tools of pressure that undermine their moral credibility. However, sustained education efforts, community compensation, and detailed contingency planning can meaningfully reduce the power of coercive migration when conditions allow.
Asked what she hopes readers, especially those outside academia, take away from the book, Greenhill emphasized “an understanding and appreciation for the frequency and real-world geopolitical and humanitarian consequences of a quite common but poorly understood phenomenon that was long . . . hiding in plain sight.” I would recommend Weapons of Mass Migration to scholars, policymakers, and students seeking to understand how moral ideals can become strategic vulnerabilities. Greenhill’s work compels readers to rethink not only how states respond to migration but also what it means to uphold moral responsibility in an interconnected world.
| Key terminology: Coercive engineered migration: The deliberate creation or manipulation of large-scale population movements to pressure another state into political or military concessions. Two-level asymmetric coercion: Greenhill’s model showing how weaker actors pressure stronger ones by turning international disputes into domestic crises, exploiting divisions and humanitarian values within target states. Challengers: Governments, rebel groups, or other actors, such as humanitarian NGOs, multinational corporations, and international organizations, use or threaten migration to influence more powerful target states through political, military, or social means. Generator: The main actor, often a state, that deliberately triggers or directs a migration crisis for political gain. Agent provocateur: A group or actor that escalates displacement to provoke outside attention or intervention. Opportunist: An actor that takes advantage of an existing migration crisis to pursue its own goals. |
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Hemispheres 