Kelly Greenhill

Kelly Greenhill is an International Relations and Security Studies scholar whose research focuses on state foreign and defence policy. In particular she looks at ‘new security challenges’, including the use of migration as a political weapon. Greenhill argues that the forced movement of displaced persons is often turned into a foreign policy instrument by states – the departure or the expulsion of unwanted citizens is effectively used to help achieve a particular goal. Hence, Greenhill refers to refugees as a ‘weapon’ whose movement can be engineered and controlled to pressurise an enemy group or government. She evocatively quotes a line attributed to Donald P. Kent in the opening of her book Weapons of Mass Migration to capture this idea: ‘one refugee is a novelty, ten refugees are boring, and a hundred refugees are a menace’.

For one of her case studies, Greenhill analyses the Mariel Boat Lift – an incident that took place in 1980 after Fidel Castro opened Cuba’s borders and allowed many Cubans (previously barred from emigrating) to travel to the United States. Many of those who fled were ordinary Cubans but Castro also pushed for the emigration of criminals, the mentally ill and other ‘unwanted’ individuals including homosexuals and prostitutes, famously boasting that he had ‘flushed our [Cuba’s] toilets on the Unites States’. Castro used the threat of this exodus and later the exodus itself as a bargaining chip to force the American government’s hand in political negotiations. The Cuban government, Greenhill finds, also made similar threats in 1965 and in 1994.

When international relations theorists talk about coercion, they are most often referring to the use of military threat but Greenhill’s work reminds us of the non-military methods which states use as instruments of persuasion, including the manipulation of migration and displacement. Greenhill calls this tactic ‘coercive engineered migration’ and in Weapons of Mass Migration she charts 56 instances where states applied this type of pressure (between 1951 and 2006). What is remarkable is that, even though most of the ‘challenger’ states were markedly weaker than the enemies or targets they threatened, they achieved their goals in 73% of these cases, making the use of forced migration an extremely popular foreign policy tactic and a powerful ‘weapon of the weak’. Most interestingly, Greenhill says, it is liberal states – normally seen as much ‘stronger’ actors in the international sphere – who are especially vulnerable to this ‘weapon’ because most of them have codified commitments to human rights and refugee protection. Liberal states have to respect these standards of protection and uphold their international reputations which makes it much harder for them to fight against coercive pressure by simply turning back weaponised refugees.

Further Reading and Resources

Greenhill’s book: Greenhill, K. (2010) Weapons of Mass Migration: Forced Displacement, Coercion and Foreign Policy, Cornell University Press.

A shorter article by Greenhill, summarising some of her case studies and her overall findings, can also be found here:

Some scholars have disagreed with Greenhill’s framing of refugees as ‘weapons’. In particular, Lev Marder makes many interesting points in an article criticising Greenhill’s metaphor of ‘the weapon’. He argues that Greenhill frames the problem of coerced migration in a highly securitised way and questions how suitable this is for the discussion of displacement. See Marder, L. (2018) ‘Refugees Are Not Weapons: The “Weapons of Mass Migration” Metaphor and Its Implications’, International Studies Review, 20 (4), pp.576-588:

You can read a brief historical overview of the Mariel Boatlift here – the article focuses on the drivers of the boatlift and its impact on the US government:


Published by Discussing Displacement

Discussing Displacement is a blog dedicated to explaining some of the key ideas and arguments within Refugee and Forced Migration Studies.

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