The imperial boomerang is the thesis that governments that develop repressive techniques to control colonial territories will eventually deploy those same techniques domestically against their own citizens. This concept originates with Aimé Césaire in Discourse on Colonialism (1950) where it is called the terrific boomerang to explain the origins of European fascism in the first half of the 20th century.^[1][2] Hannah Arendt agreed with this usage, calling it the boomerang effect in The Origins of Totalitarianism (1951).^[3][4][5] According to both writers, the methods of Adolf Hitler and the Nazi Party were not exceptional from a world-wide view because European colonial empires had been killing millions of people worldwide as part of the process of colonization for a very long time. Rather, they were exceptional in that they were applied to Europeans within Europe, rather than to colonized populations in the Global South.^[6] It is sometimes called Foucault's boomerang even though Michel Foucault did not originate the term.

In 1950, Aimé Césaire coined and described the term through his analysis of the development of violent, fascist, and brutalizing tendencies within Europe as connected to the practice of European colonialism.^[2] Césaire wrote in Discourse on Colonialism:

And then one fine day the bourgeoisie is awakened by a terrific boomerang effect: the gestapos are busy, the prisons fill up, the torturers standing around the racks invent, refine, discuss. People are surprised, they become indignant. They say: "How strange! But never mind—it's Nazism, it will pass!" And they wait, and they hope; and they hide the truth from themselves, that it is barbarism, the supreme barbarism, the crowning barbarism that sums up all the daily barbarisms; that it is Nazism, yes, but that before they were its victims, they were its accomplices; that they tolerated that Nazism before it was inflicted on them, that they absolved it, shut their eyes to it, legitimized it, because, until then, it had been applied only to non-European peoples; that they have cultivated that Nazism, that they are responsible for it, and that before engulfing the whole edifice of Western, Christian civilization in its reddened waters, it oozes, seeps, and trickles from every crack.

— Aimé Césaire, Discourse on Colonialism (1950)

In the English translation this is rendered as a "terrific boomerang";^[2] in the original French, however, Césaire did not use the term "boomerang" and instead wrote "un formidable choc en retour"—which can be literally translated as "a tremendous shock in return".^[7]

In his 1976 lecture Society Must Be Defended, Michel Foucault repeated these ideas.^[8] According to him:

[W]hile colonization, with its techniques and its political and juridical weapons, obviously transported European models to other continents, it also had a considerable boomerang effect on the mechanisms of power in the West, and on the apparatuses, institutions, and techniques of power. A whole series of colonial models was brought back to the West, and the result was that the West could practice something resembling colonization, or an internal colonialism, on itself.

Historians and social scientists have applied the concept of the imperial boomering to analyse the transnational formation of security aparatuses, focussing on the effects of the United States' overseas empire. The imperial boomerang has been invoked to explain the ongoing militarization of police and their domestic deployment in response to political protest in urban centers.^[9][10] Such deployment has proliferated worldwide,^[11][12] considering that the globalization of militarized policing continues to be a crucial aspect of contemporary foreign policy of Western colonial powers such as the United States, whose early experiments with developing comprehensive coercive state apparatuses and counterinsurgency techniques began during the American colonization of the Philippines.^[6][13][14] Focusing on how British and American colonial agents and dispatched military officials transplanted overseas counterinsurgency and police technologies back home, sociologist Julian Go argues:

We can better see how the history of policing is entangled with imperialism and recognize that what is typically called "the militarization of policing" is in an effect of the imperial boomerang—a result of imperial-military feedback.^[15]

Some scholars suggest that the directionality of the imperial boomerang needs to be re-evaluated. Political scientist Stuart Schrader argues for a colony-centered explanation to the boomerang effect, especially in the case of the United States where imperial and racial violence predates the heyday of the American empire.^[16] In her comments on Schrader's work, political scientist Jeanne Morefield writes:

Schrader's analysis goes a long way toward explaining the seemingly acephalic quality of American imperialism, a quality which contributes to its ongoing obfuscation. Behind the logic of "liberal hegemony" lies counterinsurgency and professionalized policing, modes of racialized power that structure the everyday lives of people in America and throughout the world while deflecting attention away from that power at every level.^[11]

• Imperialism
• Postcolonialism