The Use or Threat of Force by States

(p. 744) 33  The Use or Threat of Force by States

1.  Historical Overview 1815–19451

In the practice of states in nineteenth-century Europe, war was sometimes still represented as a last resort, that is, as a form of dispute settlement.2 However, the prevailing view was that resort to war was an attribute of statehood and that conquest produced title.3 Thus, the annexation of Alsace-Lorraine by the German Empire was not the object of a policy of non-recognition either by France or by third states.4 Certain other aspects of nineteenth-century practice are worth recalling. In particular there was a somewhat nebulous doctrine of intervention, which was used, to a certain extent, in conjunction with coercive measures short of a formal ‘state of war’, such as reprisals or pacific blockade. This evasion was useful both diplomatically and to avoid internal constitutional constraints on resort to war.

The approach adopted under the League of Nations Covenant of 1919 essentially reflected nineteenth-century thinking. The principal innovations were certain procedural constraints on resort to war, but, provided the procedures foreseen in Articles 11 to 17 were exhausted, resort to war was permissible. This was despite Article 10, under which members were obliged to respect and preserve as against external aggression the territorial integrity and existing independence of all members of the League.5

(p. 745) Independently of the Covenant, certain states were concerned to establish the illegality of conquest. A recommendation of the International Conference of American States at Washington in 1890 contained the principle that cessions of territory made under threats of war or in the presence of an armed force should be void.6 After 1919 the effort took the form of attempts to fill what was described as the ‘gap in the Covenant’. The Sixth Assembly of the League adopted a resolution on 25 September 1925 which stated that a ‘war of aggression’ constituted ‘an international crime’, in accordance with a Spanish proposal.7 At the Eighth Assembly a Polish proposal for a resolution prohibiting wars of aggression was adopted unanimously.8 Neither proposal was put forward as representing existing law.

A more important development was the conclusion in 1928 of the General Treaty for the Renunciation of War (the Kellogg–Briand Pact).9 By Article I the parties ‘condemn[ed] recourse to war for the solution of international controversies, and renounce[d] it as an instrument of national policy in their relations with one another’. By Article II they agreed that settlement of all disputes arising among them ‘shall never be sought except by pacific means’. The Pact had 63 states parties and is apparently still in force. Only four states in existence before the Second World War were not bound by its provisions.10

The Kellogg–Briand Pact was prominent as the foundation of the prosecution case on the count of waging aggressive war at the International Military Tribunals in Nuremberg and Tokyo.11 The Pact prefigures the legal regime of the Charter of the United Nations, providing a degree of continuity with the law of the interwar period.12

The principal parties to the Kellogg–Briand Pact made reservations, accepted by the other parties, relating to self-defence.13 The system which emerged had four elements: first, the obligation not to resort to war to solve international controversies; secondly, the obligation to settle disputes exclusively by peaceful means; thirdly, the reservation of the right of self-defence including collective self-defence, and fourthly, the reservation of the obligations of the League Covenant. Seen in its context, this was a realistic and comprehensive legal regime, which played a considerable role in practice.14 Thus, the US invoked the Pact in relation to hostilities between China and the USSR in 1929, in 1931 in relation to the conflict between China and Japan, and (p. 746) in the context of the Leticia dispute between Peru and Ecuador in 1933. The Pact continued to play a role even in 1939, when it was cited by the League Assembly in condemnation of Soviet action against Finland. Practice was not consistent, however: the Italian conquest of Ethiopia, although subject to ineffective sanctions, was accorded recognition by a number of states including the UK and France (recognition was rescinded in 1941).15

2.  The Charter Prohibition on Use or Threat of Force16

(A)  Article 2 in Context

The essentials of the Kellogg–Briand regime reappeared in the UN Charter, but subject to the important qualification that the powers of the Security Council were disjoined from the rules relating to the use of force, whereas under the Covenant the powers of the Council had been closely linked to the rubric of ‘resort to war’ in breach of the Covenant.

Article 2 formulates certain principles applicable both to the Organization and its Members. In particular:

  1. 3.  All Members shall settle their international disputes by peaceful means in such a manner that international peace and security, and justice, are not endangered.

  2. 4.  All Members shall refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any State, or in any other manner inconsistent with the Purposes of the United Nations.

  3. 7.  Nothing contained in the present Charter shall authorize the United Nations to intervene in matters which are essentially within the domestic jurisdiction of any State or shall require the Members to submit such matters to settlement under the present Charter; but this principle shall not prejudice the application of enforcement measures under Chapter VII.

Article 2(4) has been described as ‘a cornerstone of the United Nations Charter’.17 It bans the unilateral threat or use of force by states, save in certain limited circumstances.

(p. 747) But it raises acute questions of interpretation.18 The first concerns the vital subject of the provision, the ‘threat or use of force’. Even the scope of the fundamental notion of ‘force’ is not undisputed. The prevailing view, however, is that it is confined solely to armed force19 used directly or indirectly (i.e. state participation in the use of force by another state or by irregulars, mercenaries or rebels).20 It does not extend to political or economic coercion.21

While the term ‘use’ in the context of armed force is tolerably clear, the term ‘threat’ remains uncertain.22Although the prohibition is clear on its face, the threat of force remains a part of everyday life on the international plane, and state practice has demonstrated a certain tolerance of it, one reason being that some obvious threats—such as the development and stockpiling of weapons—are concomitant to the right of self-defence under Article 51 of the Charter. In addition, the threat of force is preferable to the alternative, and may even play a role in the settlement of disputes.23

Another disputed phrase in Article 2(4) is ‘against the territorial integrity or political independence of any State’. Some writers have relied on this language to propound substantial qualifications on the prohibition of the use of force,24 and in Corfu Channel the UK argued along similar lines in defending its mine-sweeping operation to collect evidence within Albanian waters. However, the preparatory work of the Charter is sufficiently clear: this phrasing was introduced precisely to provide guarantees to small states and was not intended to have a restrictive effect; the Court has consistently so held.25

(B)  The Right of Self-Defence

The most prominent exception to the prohibition on the use of force is each state’s right to defend itself. Article 51 relevantly provides:

Nothing in the present Charter shall impair the inherent right of individual or collective self-defence if an armed attack occurs against a Member of the United Nations, until(p. 748) the Security Council has taken measures necessary to maintain international peace and security.…

Article 51 reserves the ‘inherent’ right of individual or collective self-defence ‘if an armed attack occurs against a Member of the United Nations’. In Nicaragua it was recognized that this formulation refers to pre-existing customary law.26

A central difficulty in applying Article 51 is the term ‘armed attack’.27 The draft ers likely interpreted the term as encompassing the kind of conventional attack characteristic of the Second World War. The evolution of modern weapons, however, makes any rigid typology difficult to maintain.28 Modern warfare also tends to feature increased participation of irregular forces alongside or instead of state armies. In Nicaragua, drawing on the law of state responsibility and the General Assembly’s 1974 definition of ‘aggression’, the Court concluded there was general agreement that armed attack included ‘the sending by or on behalf of a State of armed bands, groups, irregulars or mercenaries’,29 ‘if such an operation, because of its scale and effects, would have been classified as an armed attack rather than as a mere frontier incident had it been carried out by regular armed forces’.30

But it is doubtful whether a state which provides aid and support to rebel groups without actually sending them against another state has committed an ‘armed attack’.31 In Nicaragua the Court was not persuaded that the provision of arms and other support to irregular groups demonstrated an armed attack by the US against Nicaragua or by Nicaragua against neighbouring states, although other illegalities (the mining of a harbour, intervention in internal affairs) had been committed.32 Such assistance may amount to a threat or use of force, or unlawful intervention,33 but falls short of ‘armed attack’ triggering the Article 51 right of self-defence.

Another criterion for ‘armed attack’ focuses on the ‘scale and effects’ of an attack, distinguishing the ‘most grave forms’ of force (armed attacks) from ‘other less grave forms’ (e.g. border skirmishes or ‘mere frontier incident[s]’).34 The gravity threshold(p. 749) was reiterated in Oil Platforms.35 There the US alleged that the gravity of an attack on one of its ships was exacerbated because it was part of a pattern of similar incidents; the Court left open whether a series of attacks could cumulatively amount to ‘armed attack’.36 The majority in Oil Platforms also found that any attack must be carried out with ‘the specific intention of harming’.37 But the addition of such criteria, based as they are on an ex post facto assessment of a state’s behaviour, is problematic; it may be difficult for a state to discern if a minor incursion is part of some larger design, or done with harmful intent.38

The meaning of ‘armed attack’ remains controversial, particularly in connection to international responses to terrorism, discussed below. Short of a dedicated resolution on the subject from the General Assembly,39 it appears that the question will be assessed on a case by case basis.40

Although the right to self-defence is established, it is not unconstrained; force used in self-defence must be necessary and proportionate.41 The International Court has reaffirmed repeatedly that these limitations apply to all forms of self-defence, individual and collective.42 In this context, necessity has generally been interpreted as meaning that the defending state must have no other option in the circumstances than to act in forceful self-defence,43 whilst proportionality requires that the size, duration, and target of the response correspond to the attack in question.44 Thus, self-defence cannot be merely punitive or retaliatory in character.

(i)  Collective self-defence

The right of collective self-defence was accepted prior to 1945 and is expressly recognized in Article 51.45Following the Iraqi attack on Kuwait, the Security Council referred in the preamble of SC Resolution 661 to the ‘inherent right of individual or collective self-defence, in response to the armed attack by Iraq against Kuwait’.46In(p. 750) Nicaragua, the Court indicated three conditions for the lawful exercise of collective self-defence. The first is that there must have been an ‘armed attack’.47 The second, procedural condition is that the victim state ‘must form and declare the view that it has been so attacked’.48 The third condition, also procedural, is that the ‘use of collective self-defence by the third State for the benefit of the attacked State…depends on a request addressed by that State to the third State’.49 It did not require (as had sometimes been argued) that the assisting states should themselves have been the subject of an armed attack. So interpreted and so procedurally limited, collective self-defence is a valuable protection for weaker states: it was the legal basis for most of the collective security arrangements of the Cold War period.50

(ii)  Anticipatory or pre-emptive self-defence

There is a long-standing controversy as to whether the Charter definitively excludes the possibility of anticipatory self-defence,51 that is, the use of force pre-emptively to avert an imminent armed attack. Since 1945 states using force have preferred to justify their actions as self-defence in response to an armed attack, rather than asserting a right of pre-emptive action.52 But when pressed, the proponents of anticipatory self-defence rely on two related propositions.53 The first is that Article 51 reserves a right of self-defence which existed in customary law and included certain anticipatory action. The problem is that the argument is incompatible with the text of Article 51 (‘if an armed attack occurs’),54 as well as the object and purpose of the Charter, which aims to restrict the capacity of states to employ force unilaterally.55

The second proposition is that the customary law was formed in the nineteenth century, in particular, as a result of correspondence exchanged by the US and Great(p. 751) Britain in the period from 1838 to 1842.56 The cause of the exchange was the seizure and destruction in 1837 in American territory by British armed forces of a vessel (the Caroline) used by private persons assisting an armed rebellion in Canada. In protesting against the incident the US Secretary of State Daniel Webster required the British government to show the existence of a

necessity of self-defence, instant, overwhelming, leaving no choice of means, and no moment for deliberation. It will be for it to show, also, that the local authorities in Canada, even supposing the necessity of the moment authorised them to enter the territories of the United States at all, did nothing unreasonable or excessive; since the act justified by the necessity of self-defence, must be limited by that necessity, and kept clearly within it.57

Lord Ashburton in his response did not dispute this statement of principle. Webster’s formula has been repeatedly cited in support of the doctrine of anticipatory self-defence but the correspondence made no difference to the legal doctrine, such as it was, of the time. Self-defence was then regarded either as synonymous with self-preservation or as a particular instance of it. The statesmen of the period used self-preservation, self-defence, necessity, and necessity of self-defence more or less interchangeably, and the diplomatic correspondence was not intended to restrict the right of self-preservation. Many works on international law both before and aft er the Caroline case regarded self-defence as an instance of self-preservation and discussed the Caroline under that rubric.

Reference to the period 1838–42 as the critical date for the customary law said to lie behind the UN Charter is anachronistic and indefensible. Whether or not custom is capable of expanding the prima facie narrow right of self-defence expressed in Article 51,58 it is also more appropriate to know the state of customary law in 1945, and it is far from clear that in 1945 the customary law was so flexible. Since 1945 the practice of states generally has been opposed to anticipatory self-defence.59 The Israeli attack on an Iraqi nuclear reactor in 1981 was strongly condemned as a ‘clear violation of the Charter of the United Nations’ in SC Resolution 487 (adopted unanimously).60 Although it has never specifically ruled on the subject, the International Court may have impliedly excluded anticipatory self-defence from the ambit of Article 51. In Armed Activities (DRC v Uganda), the Court said:

Article 51 of the Charter may justify the use of force in self-defence only within the strict confines there laid down. It does not allow the use of force by a State to protect perceived (p. 752) security interests beyond those parameters. Other means are available to a concerned State, including, in particular, recourse to the Security Council.61

The concept of anticipatory self-defence has seen a revival in the literature with the prosecution of the so-called War on Terror. The Bush administration denounced the ‘reactive posture’ of the past, refusing to wait for enemies such as ‘rogue states and terrorists’ to strike first and announcing its readiness to act to prevent threats from potential adversaries, even in the face of uncertainty as to the time and place of an attack.62 This goes further than pre-emptive self-defence into the realm of preventive self-defence; it lacks any legal basis and is not generally accepted.63 It may be noted that when the US Expeditionary Force began military operations against Iraq in March 2003, the letter to the Security Council of 20 March 2003 relied upon Security Council resolutions as the primary putative legal basis of the action, not on any right to preemptive or preventive self-defence under general international law.64

(iii)  Humanitarian intervention65

Another debate over the scope of Article 2(4) concerns forcible measures of so-called ‘humanitarian intervention’.66 By the end of the nineteenth century most publicists admitted that a right of humanitarian intervention existed. A state which had abused its sovereignty by brutal and excessively cruel treatment of those within its power was regarded as having made itself liable to action by any state which was prepared to intervene. The action was in the nature of a police measure, and no change of sovereignty could result. Some writers restricted it to action to free a nation oppressed by another; some considered its object to be to put an end to crimes and slaughter; some referred to ‘tyranny’, others to extreme cruelty; some to religious persecution, and, lastly, some confused the issue by considering as lawful intervention in case of feeble government or ‘misrule’ leading to anarchy.67

(p. 753) Much of the time, however, humanitarian intervention appeared as a cloak for episodes of imperialism, including the US invasion of Cuba in 1898, and the doctrine of humanitarian intervention did not survive the post-1919 era. For example, the Indian intervention in Bangladesh (1971), the Tanzanian action in Uganda (1979), and the Vietnamese invasion of Cambodia (1979) were all possible examples of humanitarian intervention, but in all three cases the belligerents chose to justify their actions under the rubric of self-defence.68

The issue was raised once more with the NATO bombing of targets throughout Yugoslavia in March to May 1999. There is a preliminary difficulty in that, beginning in October 1998, the threats of force were linked directly to a collateral agenda, that is, the acceptance by Yugoslavia of various ‘demands’ concerning the status of Kosovo. This background has been ignored by many commentators.

The UK position was set out in a statement by the Permanent Representative to the United Nations on 24 March 1999. He said:

The action being taken is legal. It is justified as an exceptional measure to prevent an overwhelming humanitarian catastrophe. Under present circumstances in Kosovo there is convincing evidence that such a catastrophe is imminent. Renewed acts of repression by the authorities of the Federal Republic of Yugoslavia would cause further loss of civilian life and would lead to displacement of the civilian population on a large scale and in hostile conditions. Every means short of force has been tried to avert this situation. In these circumstances, and as an exceptional measure on grounds of overwhelming humanitarian necessity, military intervention is legally justifiable. The force now proposed is directed exclusively to averting a humanitarian catastrophe, and is the minimum judged necessary for that purpose.69

This statement clearly asserted the action was legal but invoked no specific international law source; in particular, no reference is made to the UN Charter.

The position in 1999, when the operations took place, was that there was little or no authority or state practice to support the right of individual states to use force on humanitarian grounds.70 The weak legal position was recognized by the UK when it informed the Select Committee on Foreign Affairs of the House of Commons of its aim of establishing in the UN ‘new principles governing humanitarian intervention’.71

Three months after the NATO action against Yugoslavia had ended, the Foreign Ministers of the G77

stressed the need to maintain clear distinctions between humanitarian assistance and other activities of the United Nations. They rejected the so-called right of humanitarian intervention, which had no basis in the UN Charter or in international law.72

(p. 754) Those who espouse the right of humanitarian intervention tend to ignore state practice. Instead, reliance is placed upon a number of ambiguous episodes, which, it is said, either presage or constitute a change in the customary law.73 In addition, reference is oft en made to the need to balance human rights against the prohibition of the use of force in the international legal order. Worthy though such an impulse may be, it runs into the same obstacle as the argument for anticipatory self-defence: there is simply no room for it within the regulatory space established by Articles 2(4) and 51 of the Charter.74

The material relied upon includes three problematic developments. The first was the Air Exclusion Zone in northern Iraq, created in 1991. This involved using force with the object of excluding Iraqi air power in order to protect the Kurds of northern Iraq. This was, in the view of the British government, justified by ‘the customary international law principle of humanitarian intervention’.75 Again no sources were provided to support this view. The Air Exclusion Zone in southern Iraq, created in 1992, was also controversial but was, unlike its predecessor, purportedly based upon SC Resolution 668 of 1990.76 The UK position over the life of the no-fly zones was, however, inconstant; on occasion, it claimed that both zones were supported by the resolution; in other instances, it claimed that even without the resolution, both zones could be justified under the supposed principle of humanitarian intervention.77

The third episode is the operations authorized by the Economic Community of West African States (ECOWAS) in Liberia in 1990.78 The operations (by the Economic Community of West African States Monitoring Group) were a regional peacekeeping exercise which, at a certain stage, received the support of the Security Council and the Organization of African Unity.79 Contemporary observers did not recognize the episode as a case of humanitarian intervention. The practical basis of the action was the need to restore order in a state without an effective government. The ‘practice’, such as it is, involves a small number of adherent states, and contemporary debates in the Security Council reveal marked divisions of opinion.80

(iv)  Intervention to rescue nationals81

International law in the Charter era contains multiple instances of a state utilizing force within another’s territory in order to rescue its nationals. Some writers argue the(p. 755) right to protect nationals by the use of force is an aspect of the customary law right of self-defence,82but again this is doubtful.83 The protection of nationals was one of several justifications invoked by the US in relation to the use of force against Panama in 1989.84 Further examples abound,85 including, inter alia, the joint US–Belgian operation in the Congo in 1964,86 the landing of US troops in the Dominican Republic in 1965,87 the 1976 rescue of Israeli nationals at Entebbe Airport in Uganda,88 Operation Eagle Claw, the aborted attempt to resolve the Iranian hostage crisis in 1980,89 and the purported rescue of US medical students in Grenada in 1983.90 France intervened in a variety of central and western African nations from 2002 onwards.91More recently, Russia has claimed this right with respect to its 2008 conflict with Georgia.92

(v)  The ‘responsibility to protect’93

Less a doctrine of its own than a refocusing of humanitarian intervention, the term ‘responsibility to protect’ emerged in 2001 in a Report of the International Commission on Intervention and State Sovereignty (ICISS).94 It was subsequently adopted in several other United Nations documents, most notably the General Assembly’s 2005 World Summit Outcome.95 In essence, it is intended to permit (and even require) international action in the face of the most serious human rights abuses or international crimes, in cases where a state fails in its duty to protect its own citizens.96 Although originally (p. 756) labelled a ‘new approach’97 or a ‘recharacterization of sovereignty’,98 support for the concept gathered speed, to the extent that it was soon considered by some to be an emerging norm of international law.99 The 2001 Report purported to identify three situations where the ‘residual responsibility’ of the states to take action was activated: (a) when a particular state is clearly unwilling or unable to fulfil its responsibility to protect; (b) where a particular state is itself the perpetrator of crimes or atrocities; or (c) where people living outside a particular state are directly threatened by actions taking place there.100 This was rendered more generally in the 2005 World Summit Outcome:101

In this context, we are prepared to take collective action, in a timely and decisive manner, through the Security Council, in accordance with the Charter, including Chapter VII, on a case-by-case basis and in cooperation with relevant regional organizations as appropriate, should peaceful means be inadequate and national authorities are manifestly failing to protect their populations from genocide, war crimes, ethnic cleansing and crimes against humanity.

But it remains clear that the responsibility to protect cannot be used within the framework of Articles 2(4) and 51 to justify the unilateral use of force. The various resolutions and statements endorsing the concept do so subject to the crucial qualifier that collective security and the UN system remain the primary forum for military action.102

The Security Council has been receptive to the nascent doctrine, highlighting that states have a responsibility to protect their own citizens in relation to the situation in Sudan (though not commenting on the capacity of other states to intervene),103 and more dramatically, authorizing the collective use of force under Chapter VII against Libya.104 As such, the concept reflects an evolution in the way the Security Council views its powers under Articles 39 and 42 of the Charter. Thus the ‘responsibility to(p. 757) protect’ cannot justify the unilateral use of force, but may justify collective measures within the Charter system. This leaves an underlying concern unaddressed. Thus Tomuschat asks:

[M]ust the international community stand idly by whilst millions of human beings are massacred just because in the Security Council a permanent member holds its protective hands over the culprit? Must national sovereignty be understood as the paramount rule of international law that overrides any other value? Giving an affirmative response to these two questions would totally deprive international law of its essential value content.105

As a statement about the political landscape this seems persuasive. But the prohibition of the use of force as established in the post-war period was designed to prevent precisely this kind of adventure, and the overall record of high-minded intervention is dismal. At any rate it cannot be said that any new exception to Charter prohibitions has been authoritatively articulated, still less generally accepted.106

3.  Authorizing the Use of Force: the Security Council

The United Nations presents itself as a comprehensive public order system. Despite persistent weaknesses in multilateral decision-making, the Security Council has primary responsibility for enforcement action to deal with breaches of the peace, threats to the peace or acts of aggression. Individual member states have the right of individual or collective self-defence, but only ‘until the Security Council has taken measures necessary to maintain international peace and security’. In the case of regional organizations the power of enforcement is in certain conditions delegated by the Security Council to the organizations concerned.

Enforcement action may involve the use of force against a state. However the practice has evolved of authorizing peacekeeping operations which are contingent upon the consent of the state whose territory is the site of the operations. The roles of peacekeeping and enforcement action have on occasion become confused, with unfortunate results.

Certain corollaries to the legal regime have developed, with significance independently of questions of institutional design. They include: (a) the principle of non-recognition of territorial acquisitions obtained by use or threat of force;107 and(p. 758) (b) the principle that a treaty procured by the threat or use of force in violation of the Charter is void.108 Certain corollaries are also expressed in the ILC’s 2001 Articles on the Responsibility of States for Intentionally Wrongful Acts.109 The appearance of such corollaries suggests an evolution in the direction of greater consistency, such as one would expect of a public order system at national level. But such great expectations, though long held,110 have often been frustrated, and it remains true that the legal regime of enforcement has at its heart a broad collective discretion fettered by an unaccountable veto.

(A)  The Role of the Security Council111

The Security Council is the keystone of the UN system of collective security, bearing ‘primary responsibility for the maintenance of international peace and security’ under Article 24(1) of the Charter.112 An essential part of its mandate is its monopoly over the authorization of the use of force, pursuant to Chapter VII.113 In so doing, the Security Council acts on behalf of the Members, who agree to accept and carry out the decisions of the Security Council (Articles 25 and 48); further, binding decisions of the Council, being obligations under the Charter, prevail over obligations contained in any other agreement (Article 103), though presumably not over peremptory norms.114

The Security Council has 15 members, five of them permanent and with a power of veto over any non-procedural decision.115 This perpetuates the Grand Alliance that emerged victorious from the Second World War: the US, the UK, France, Russia (previously the USSR), and the People’s Republic of China. The remaining 10 members are elected from the members of the General Assembly for two-year terms, and may not be immediately re-elected. Every year, five positions on the Security Council become available.

(p. 759) The drafters of the Charter intended the Security Council to be the central enforcement organ of the United Nations. The subsequent breakdown of relations between the USSR and the western powers resulted in a deadlock, and the Security Council was largely ineffective until the end of the Cold War.116 The permanent members of the Security Council co-operated in response to the Iraqi invasion of Kuwait,117 and the subsequent prosecution of the first Gulf War. The capacity for co-operation has been somewhat variable since then, with the co-ordinated reaction to the 11 September 2001 attacks on the US118 disintegrating with the US invasion of Iraq in 2003.119 More recently, the Security Council has demonstrated again its capacity for meaningful action with its intervention in the Libyan insurgency.120

(B)  Determination Prior to the Authorization of Force: Article 39

Within the UN system, the Security Council is the sole body with the capacity to authorize the use of force. The taking or authorizing the use of force is only one of several measures available to the Council under Chapter VII. The starting point is Article 39, which provides:

The Security Council shall determine the existence of any threat to the peace, breach of the peace or act of aggression and shall make recommendations, or decide what measures should be taken in accordance with Articles 41 and 42, to maintain or restore international peace and security.

Only those resolutions that are intra vires the Charter acquire binding force on Members under Article 25, which speaks of ‘decisions of the Security Council ‘in accordance with the present Charter’. To this end, Article 39 functions as the gateway to Chapter VII: before taking action, the Council must first determine the existence of a threat to or breach of the peace, or an act of aggression. But the Council enjoys wide discretion.121 Article 39 sets no express limits, and it is difficult to think of realistic scenarios in which such determinations would be justiciable.122

(p. 760) (i)  ‘Threat to the Peace’123

The notion of a threat to the peace is mercurial: it raises the possibility of multiple perspectives as to what constitutes a threat,124 a position which led the International Criminal Tribunal for the Former Yugoslavia (ICTY) in the Tadić case to note that declaration of a threat entails a factual and political judgment, not a legal one.125A threat to the peace is, practically speaking, the only Article 39 declaration needing to be made by the Security Council.126

At its most basic, the concept is intended to enable a response to imminent armed conflict between states.127Severe intrastate violence (such as the Balkan War prior to the splintering of Yugoslavia),128 serious violations of human rights and humanitarian law (such as in Somalia and other east/central African nations during the early 1990s),129 and terrorism130 have also been designated as threats to the peace.

The concept has been further expanded to include not only situations in which the use of armed force appears imminent, but those where factors subsist that may lead to the use of force. In 1992, the President of the Security Council stated that ‘[t]he absence of war and military conflicts amongst states does not in itself ensure international peace and security. Non-military sources of instability in the economic, social, humanitarian and ecological fields have become “threats to peace and security” ’.131 The Security Council has yet to expressly utilize this ‘expanded’ mandate.

(ii)  ‘Breach of the peace’

A breach of the peace within the meaning of Article 39 is typically characterized by hostility between the armed units of two states.132 Since the term focuses on the(p. 761) point at which hostilities commence, it accordingly becomes irrelevant if one side is defeated quickly thereafter. In SC Resolution 502, the Security Council considered the Argentine invasion of the Falklands to be a breach of the peace even prior to the UK’s counter-offensive.133 A similar determination was made following the Iraqi invasion of Kuwait in 1990.134

(iii)  ‘Act of aggression’

In 1974 the General Assembly adopted Resolution 3314 on the definition of aggression. It defines ‘aggression’ broadly as:135

the use of armed force by a state against the sovereignty, territorial integrity or political independence of another state or in any other manner inconsistent with the Charter of the United Nations, as set out in this definition.

Article 2 provides that the first use of armed force by a state in contravention of the Charter constitutes prima facie evidence of an act of aggression (though the Security Council may determine otherwise based on relevant circumstances, including the gravity of the alleged act). The substance of the definition is contained principally in Article 3, which lists a series of acts considered instances of aggression. Noteworthy is the final paragraph, which covers:

  1. (g)  The sending by or on behalf of a state of armed bands, groups, irregulars or mercenaries, which carry out acts of armed force against another state of such gravity as to amount to the acts listed above, or its substantial involvement therein.

The phrase ‘or its substantial involvement therein’ indicates that the formulation extends to the provision of logistical support,136 even if the Court in Nicaragua was unwilling to permit such an extension with respect to the definition of ‘armed attack’ under Article 51.

As a somewhat dated, non-binding resolution, GA Resolution 3314(XXIX) might have been increasingly disregarded.137 However, the International Criminal Court (ICC) Assembly of States Parties in 2010 adopted a definition of the crime of aggression for the purposes of the Rome Statute of the International Criminal Court.138 Notably, Article 8bis(2) provides that acts of aggression which may generate individual criminal responsibility for the crime of aggression139 are the same as those contained in Article 3 of GA Resolution 3314. To this is added the more general perambulatory(p. 762) definition of ‘the use of armed force by a State against the sovereignty, territorial integrity or political independence of another State, or in any other manner inconsistent with the Charter of the United Nations’, derived from Article 1 of Resolution 3314 and Article 2(4) of the Charter.

(C)  Responses to the Threats to or Breaches of the Peace

Following an Article 39 determination, the Security Council may decide that provisional (Article 40), non-forcible (Article 41), or forcible (Article 42) measures shall be taken to maintain or restore international peace or security. In exercising its Chapter VII powers, the Council is subject to certain constitutional limitations.140 It ‘shall act in accordance with the Purposes and Principles of the United Nations’ (Article 24(2)), and is presumably bound by peremptory norms (though not international law more generally).141 In addition, it is limited by strictures of necessity and proportionality.

(i)  Provisional Measures: Article 40142

Before making recommendations or deciding on measures under Article 39, the Security Council may order the imposition of provisional measures under Article 40. Unlike the balance of Chapter VII, Article 40 was used with some regularity during the Cold War period, a situation that has not changed with the dissolution of the USSR.143

The relationship between Article 39 and Article 40 is not clearly delineated. The practice of the Security Council, however, supports the notion that an Article 39 determination is a precondition to provisional measures.144

Provisional measures leave unaffected the legal position of the parties to the dis-pute.145 Thus the Security Council could not call on a Member to acknowledge its own breach of Article 2(4) or its violation of another Member’s territorial sovereignty. It can, however, call on Members to observe a ceasefire or withdraw troops from certain areas.146 Whether measures under Article 40 are binding on Members depends on(p. 763) the interpretation of the resolution; certainly they can be.147 But particularly when considering a provisional measure requiring a ceasefire, compliance vis-à-vis one belligerent is in practice conditioned on the reciprocity of the other, even if the resolution is framed in absolute terms.148

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