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From Jus ad Bellum to Jus ad Vim: Recalibrating Our Understanding of the Moral Use of Force


In the preface of the 2006 edition of Just and Unjust Wars, Michael Walzer makes an important distinction between, on the one hand, “measures short of war,” such as imposing no-fly zones, pinpoint air/missile strikes, and CIA operations, and on the other, “actual warfare,” typified by a ground invasion or a large-scale bombing campaign. Even if the former are, technically speaking, acts of war according to international law, he proffers that “it is common sense to recognize that they are very different from war.” While they all involve “the use of force,” Walzer distinguishes between the level of force used: the former, being more limited in scope, lack the “unpredictable and often catastrophic consequences” of a “full-scale attack.” Walzer calls the ethical framework governing these measures jus ad vim (the just use of force), and he applies it to state-sponsored uses of force against both state and nonstate actors outside a state's territory that fall short of the quantum and duration associated with traditional warfare. Compared to acts of war, jus ad vim actions present diminished risk to one's own troops, have a destructive outcome that is more predictable and smaller in scale, severely curtail the risk of civilian casualties, and entail a lower economic and military burden. These factors make jus ad vim actions nominally easier for statesmen to justify compared to conventional warfare, though this does not necessarily mean these actions are morally legitimate or that they do not have potentially nefarious consequences.

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Alex J. Bellamy , “Is the War on Terror Just?International Relations 19, no. 3 (September 2005), pp. 275–96

Alex J. Bellamy , “When Is it Right to Fight? International Law and Jus ad Bellum,” Journal of Military Ethics 8 (September 2009), pp. 231–55

Bradley Jay Strawser , “Moral Predators: The Duty to Employ Uninhabited Aerial Vehicles,” Journal of Military Ethics 9, no. 4 (December 2010), pp. 342–68

James Turner Johnson , “Humanitarian Intervention after Iraq: Just War and International Law Perspectives,” Journal of Military Ethics 5, no. 2 (August 2006), pp. 114–27

John Williams , “Space, Scale and Just War: Meeting the Challenge of Humanitarian Intervention and Trans-National Terrorism,” Review of International Studies 34, no. 4 (October 2008), pp. 581600; p. 598

Sarah Kreps and John Kaag , “The Use of Unmanned Aerial Vehicles in Contemporary Conflict: A Legal and Ethical Analysis,” Polity 44, no. 2 (April 2012), pp. 260–85; pp. 278 and 280

Michael Walzer , “On Fighting Terrorism Justly,” International Relations 21, no. 4 (December 2007), pp. 480–84; p. 480

Kenneth Anderson , “Efficiency in Bello and ad Bellum: Making the Use of Force Too Easy?” in Claire Finkelstein and Jens David Ohlin , eds., Targeted Killings: Law and Morality in an Asymmetric World (Oxford: Oxford University Press, 2012), pp. 374402; p. 388

Martin Shaw , “Risk-Transfer Militarism, Small Massacres and the Historical Legitimacy of War,” International Relations 16, no. 3 (December 2002), pp. 343–59 and pp. 354–55

Anthony Burke , “Just War or Ethical Peace? Moral Discourses of Strategic Violence After 9/11,” International Affairs 80, no. 2 (March 2004), pp. 229353; p. 330

Alexander Benard , “Lessons from Iraq and Bosnia on the Theory and Practice of No-Fly Zones,” Journal of Strategic Studies 27, no. 3 (September 2004), pp. 454–78

Michael Walzer , “Regime Change and Just War,” Dissent 53, no. 3 (Summer 2006), pp. 103–108

Thomas Hurka , “Proportionality in the Morality of War,” Philosophy and Public Affairs 33 (January 2005), pp. 3466; p. 37

Frances V. Harbour , “Reasonable Probability of Success as a Moral Criterion in the Western Just War Tradition,” Journal of Military Ethics 10, no. 3 (September 2011), pp. 230–41; pp. 231 and 234

James Pattison , “The Ethics of Humanitarian Intervention in Libya,” Ethics & International Affairs 25, no. 3 (Fall 2011), pp. 17

Davis Brown , “Proportionality in Modern Just War Theory: A Tort Based Approach,” Journal of Military Ethics 10, no. 3 (September 2011), pp. 213–29; pp. 216–17

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Ethics & International Affairs
  • ISSN: 0892-6794
  • EISSN: 1747-7093
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