Use of force is a politically sensitive and legally undetermined topic. It is therefore not surprising that it constitutes a highly controversial issue. During the Cold War, various critical debates about the legality of military interventions (Korea, Vietnam, Nicaragua, Palestine, Afghanistan) were prevalent. These controversies did not disappear in the 1990s (Yugoslavia) nor in the 2000s and 2010s (Afghanistan, Iraq, Israel/Lebanon, Russia/Georgia, Libya, Syria, Ukraine, among others). A general assessment of the numerous books and articles dedicated to this issue reveals a deep ambivalence. On the one hand, no one really contests that the use of force is strictly forbidden in contemporary international law. This prohibition is recognized as a core rule of the law of nations, and even a rule of imperative international law (jus cogens). Indeed, it seems difficult to conceive any kind of legal order without at least affirming that its subjects cannot attack one another. The prohibition of the use of force is also logically linked to the notion of external sovereignty, aiming both at protecting the identity and the personality of every state and at preserving individuals “from the scourge of war” (preamble of the UN Charter). On the other hand, there are, to say the least, a great variety of interpretations of the rule. Are collective security and self-defense the only exceptions in allowing states to use force? Is the Security Council the only authority able to authorize states to use force? Under what conditions are states able to invoke self-defense? Those questions seem difficult to address, as the conventional sources are rather limited: Article 2(4) and Chapters VII and VIII of the UN Charter are far from providing explicit answers to all the questions raised. Thus, the answers can be found mainly in customary international law, with all the difficulties surrounding the task of establishing that law.
Two major trends can be distinguished in international legal scholarship. On the one hand, we find extensive interpretations of the possibilities to use force: broad definition of self-defense, a rejection of a UN monopoly to authorize military actions, and the admissibility of humanitarian or pro-democratic interventions. These writings are generally grounded in a nonpositivist approach to international law. Considerations of morality or politics are taken into account to support some of the arguments presented, including recent examples such as increasing threats posed by terrorists and rogue states; the emergence of values of democracy, rule of law, and human rights; and a “moralization” of international law, among others. On the other hand, many authors prefer a legally and textually oriented method to assess the rule. Customary international law must be interpreted according to the UN Charter, to relevant subsequent instruments (GA Resolutions 2625 (XXV), 3314 (XXIX), 42.22, 60/1, . . .), and to judicial decisions, especially from the International Court of Justice (ICJ) (Nicaragua, Oil Platforms, Armed Activities on the Territory of the Congo cases). Generally, these authors explicitly or implicitly contend that broadening the possibilities to use force in the name of policy considerations would be too dangerous, as it would lead to a revival of ancient “just war” theories, opening the door to arbitrariness, subjectivity, and imperialism of the major powers. Of course, many authors cannot be situated in either the first (the “extensive approach”) or the second (the “restrictive approach”) category defined above. Nevertheless, it is always possible, and often useful, to place every book or article dedicated to the use of force on a spectrum running from one trend to the other. Arend and Beck 1993, Dinstein 2011, and Franck 2002 constitute good illustrations of the extensive approach, whereas Gray 2008, Henderson 2010, and Corten 2010 can be characterized as “restrictive.” Kolb 2009 is perhaps more difficult to classify, whereas Weller 2014 offers an overview of various authors pertaining to different approaches. Lastly, it must be kept in mind that most of these books contain developments on many topics related to the use of force, in particular those subjects that are detailed in subsequent sections, including threat, consent, collective security, self-defense, and humanitarian intervention.
Arend, Anthony Clark, and Robert J. Beck. International Law and the Use of Force. London: Routledge, 1993.
Corten, Olivier. The Law against War. Oxford: Hart, 2010.
Grounded in numerous and extensive footnotes, this book offers a clear expression of the restrictive position. Arguments used to justify a use of force by broadening the possibilities enshrined in the UN Charter are refuted as being unacceptable to the majority of states. An update and translation of the original text in French (Le droit contre la guerre [Paris: Pedone, 2008], second updated edition in 2014).
Dinstein offers a comprehensive theory of the jus contra bellum, stressing the possibilities left open in contemporary international law to use force. The theses of this classical book are strong and even sometimes radical, but they are presented with a real subtlety. Also interesting due to the will of the author to address practical problems and sketch precise solutions to solve them.
Franck, Thomas. Recourse to Force: State Action against Threats and Armed Attacks. Cambridge, UK: Cambridge University Press, 2002.
This book is an interesting example of an extensive approach as defined above. Franck argues that the evolution of custom reveals a tendency to accept the legality of many actions conducted in the name of self-defense, humanitarian intervention, or even countermeasures. He also supports the concept of mitigation, which condones some limited violations of the UN Charter.
Gray, Christine. International Law and the Use of Force. 3d ed. Oxford: Oxford University Press, 2008.
Gray is distinguished from Dinstein and Franck by her stricter legal methodology. She insists on the practice, and the will, of states to show that various doctrinal intents aiming at relaxing the prohibition on the use of force have failed. Every precedent is studied with accuracy on the basis of an extensive research in official documents. Also contains an in-depth discussion of contemporary debates developing in the field.
Henderson, James. The Persistent Advocate and the Use of Force: The Impact of the United States upon the jus ad bellum in the Post–Cold War Era. Farnham, UK: Ashgate, 2010.
Henderson supports a restrictive interpretation of the relevant provisions of the UN Charter, arguing that those articles have not be modified in spite of the new interpretations supported by the United States and some of its allies.
Kolb, Robert. “Ius contra bellum.” In Le droit international relatif au maintien de la paix. 2d ed. By Robert Kolb, 435. Brussels: Bruylant/Helbing & Lichtenhahn, 2009.
Accessible book, based on a course given on the topic. After having offered a historical overview of the emergence of the Charter regime, Kolb generally supports a strict obligation to respect jus contra bellum even if, at the same time, he occasionally uses moral or pragmatic arguments to interpret the legal regime in a teleological way.
Weller, Marc, ed. The Oxford Handbook of the Use of Force in International Law. Oxford: Oxford University Press, 2014.
This handbook offers an extensive overview of many relevant issues written by top authors in the field. It includes general topics (history and theory of international law regarding the use of force, status of the rule, relations with other rules and regimes, among others) as well as detailed studies about more particular questions (collective security, cyber force, self-defense, among others).