States Only

In the first place, the prohibition in article 2(4) binds only States, as confirmed by State practice and case law.Footnote ² With respect to the parallel customary rule, it is an interesting question whether the customary prohibition also applies only to States or if it also binds non-State actors, international organisations or individuals.Footnote ³

Member States Only

As a treaty, the provisions of the UN Charter are clearly binding on its parties, that is, the Member States of the United Nations. Non-Member States are bound by the prohibition only indirectly through the UN Charter (since they could be subject to enforcement action/sanctions for failing to comply with the relevant principles),Footnote ⁴ but the source of their legal obligation is customary international law.

Use of Force by Non-State Armed Groups

In certain circumstances, State support or involvement in forcible acts of other States, or in forcible acts of non-State actors against another State will violate the prohibition of the use of force.Footnote ⁵ However, this is relevant not to who are the addressees of the prohibition (States) but to what acts or level of support will result in attribution to a State or amount to an indirect ‘use of force’ in violation of article 2(4). With respect to attribution, the general principles of State responsibility apply, as set out in articles 4 to 11 of the International Law Commission (ILC) Articles on State Responsibility. In particular, article 8 of the ILC Articles on State Responsibility provides that:

The International Court of Justice (ICJ) had applied a similar standard of attribution in the Nicaragua case, in which it held that:

Although the International Criminal Tribunal for the former Yugoslavia in the Tadic case applied a different test for attribution of ‘overall control’,Footnote ⁷ this has been criticised by both the ILCFootnote ⁸ and the ICJ, which declined to adopt this standard.Footnote ⁹ Other forms of support that do not meet the standard for attribution of the conduct of the non-State armed group to a State may nevertheless constitute an indirect ‘use of force’ by a State under article 2(4) of the UN Charter. Indirect force is discussed further in Chapter 5.

Another State?

The wording of article 2(4), in particular the terms ‘international relations’ and ‘in any other manner’, does not explicitly require the damage to be to another State.Footnote ¹¹ The reference to ‘international relations’ implies that a prohibited use of force must affect the relations between the State using force and another State. This leaves open the possibility that the actual damage is not to a State but affects inter-State relations. With respect to the phrase, ‘in any other manner’, the second half of article 2(4) was introduced to prevent loopholes in interpretation (see discussion of this term later in the chapter). Thus, interpreting the term ‘international relations’ to prohibit another type of use of force (in addition to uses of force against the territorial integrity or political independence of a State) would comply with this intended purpose of making the prohibition more expansive. Furthermore, a natural reading of the second part of article 2(4) is to read the listed elements conjunctively (i.e. as alternatives). This would result in the following categories of prohibited conduct: firstly, uses of force in the international relations of Members against the territorial integrity or political independence of any State, and secondly, uses of force in the international relations of Members in any other manner inconsistent with the Purposes of the United Nations.Footnote ¹²

This interpretation would potentially encompass a use of force that is in ‘international relations’ outside the context of State damage, such as damage to terra nullius. Claus Kreß notes that ‘[i]t is an unsettled question whether the use of force by a state … on terra nullius occurs in international relations and thus within the meaning of article 2(4) of the UN Charter’.Footnote ¹³ Since there are hardly any areas of terra nullius (rare examples include Bir Tawil between Egypt and Sudan, an area that neither claims, and parts of Antarctica), this issue is unlikely to be raised in practice. However, both on Earth (with respect to the high seas)Footnote ¹⁴ and in outer space (with respect to celestial bodies),Footnote ¹⁵ there are vast areas which do not form part of the territory of any State and are not subject to claims of sovereignty, so it is conceivable that a ‘use of force’ could be directed against these environments (for instance, as part of a malicious attack, or in the process of exploiting natural resources located in these environments), thus raising the question of whether such an act occurs in ‘international relations’ even though no State suffers direct damage.

Political Context

If there is a pre-existing dispute between the States concerned, such as contested territory, this may bring the use of force within the realm of ‘international relations’ and thus within the scope of the jus contra bellum.Footnote ³³ The political context may be relevant to whether the act itself constitutes a ‘use of force’, since it may increase the gravity of the act and indicate a hostile or coercive intention. A pre-existing dispute between States or otherwise hostile relations could thus explain why friendly States do not view certain acts as an unlawful ‘use of force’, which, if committed by an unfriendly State, would be so regarded. The State experiencing the forcible act (the ‘victim’ State) will interpret the intention or motivation of the forcible act and the perceived threat to its security (gravity) taking into account this political context; thus, the interpretation of the situation is influenced by this context, meaning that the State could in fact be applying the same criteria for a ‘use of force’ but to differently viewed ‘facts’. For example, when on 1 March 2007, 170 Swiss Army infantry troops armed with rifles lost their bearings and crossed the border into Liechtenstein, the incursion did not provoke any official protest.Footnote ³⁴ It is easy to imagine that the response and legal characterisation of such an incursion would be vastly different if it occurred between States with heightened tensions or pre-existing disputes, such as India/Pakistan or Democratic People’s Republic of Korea/South Korea. The relationship between intention, gravity and international relations is explored further in Chapter 8. A ‘use of force’ in the context of an existing international dispute may also relate to whether the act is ‘in any other manner inconsistent with the Purposes of the United Nations’ (the second part of article 2(4), discussed later), since such a use of force is inconsistent with the Purpose to maintain international peace and security through the peaceful settlement of international disputes (article 1(1), UN Charter).

The remainder of this section will look at particular categories of acts falling within and outside the scope of the term ‘international relations’.

Extra-Territorial Sovereign Manifestations of a State

The classic paradigm is a use of force by a State on the territory of another State,Footnote ³⁵ but ‘international relations’ also covers a use of force against an extraterritorial sovereign manifestation of a State including on the high seas or on the territory of the State using force, such as armed forces or embassies.Footnote ³⁶

Disputed Territory and Armistice Lines

In the case of disputed territory that is claimed by more than one State, the prohibition of the use of force acts in favour of the State in de facto control of the territory even against the State holding the sovereign title.Footnote ³⁷ This is an example of a use of force against another State that does not violate its territorial integrity. Kreß suggests that what is being protected by the prohibition in such a case is ‘the peaceful common life on the disputed territory and the maintenance of international peace and security’.Footnote ³⁸ However, this interpretation is without prejudice to the right of a victim State to act in self-defence against a State that has established military occupation over its territory as a result of an armed attack under article 51;Footnote ³⁹ a State may not use force against a State in de facto control of its territory unless it is in self-defence or with UN Security Council authorisation.Footnote ⁴⁰ A ‘use of force’ is also in ‘international relations’ and falls within the scope of article 2(4) if it ‘“violate[s] international lines of demarcation, such as armistice lines, established by or pursuant to an international agreement to which it is a party or which it is otherwise bound to respect”, provided that these lines run between two states’. Kreß argues that in the case of disputed territory and armistice lines, ‘international law subordinates the protection of territorial sovereignty to the protection of a peaceful common life on a certain piece of territory and the maintenance of international peace and security’.Footnote ⁴¹ With respect to entities whose statehood is disputed (e.g. North and South Vietnam during the Vietnam War; North and South Korea during the Korean War; Taiwan; Kosovo; Abkhazia; South Ossetia), the situation is more complicated. The jus contra bellum does not require all States to recognise the statehood of the entity in question, and it is an open question if article 2(4) covers a use of force violating an ‘international demarcation line delimiting the territory of a non-State political entity’.Footnote ⁴²

Use of Force by a State within Its Own Territory

An interesting question is raised as to whether and when a use of force by a State within its own territory is in ‘international relations’ and falls within the scope of article 2(4). Differing views were expressed on the inclusion of the use of force within a State within the scope of the prohibition during the drafting of the 1970 Friendly Relations Declaration. In the 1966 meeting of the Special Committee on Principles of International Law concerning Friendly Relations and Co-operation among States (‘Special Committee’), one representative suggested the Special Committee include a statement that ‘the prohibition on the threat or use of force did not in any way affect the use of force within a State’.Footnote ⁴³ In the 1970 meeting of the Special Committee,

However, this point was not further discussed and does not appear in the text of the Friendly Relations Declaration.

The use of force within a State’s own territory can be further broken down into several types of incidents, namely, a use of force by a State in its own territory: (a) against its own population, (b) against territorial incursion by the armed forces of another State, and (c) against foreign private actors such as individuals, merchant vessels or civilian aircraft. These are briefly dealt with in turn in the following sections.

Conclusion

In sum, it is generally agreed that the following uses of force by a State are usually in its ‘international relations’ and therefore fall within the scope of article 2(4):

• Use of force on the territory of another State or against its extraterritorial sovereign manifestations.

• Use of force to reclaim disputed territory not within de facto control.

• Use of force in violation of international demarcation lines.

• Use of force directly arising from a political dispute between States.

It is also generally accepted that the following uses of force by a State are not in its ‘international relations’ and therefore usually fall outside the scope of article 2(4):

• Use of force by a State within its own territory against its own population.

• Use of force by a State in the exercise of its law enforcement jurisdiction against private foreign actors absent other factors (such as an existing international dispute, excessive force, coercive intent, or lack of sufficient connection to law enforcement jurisdiction).

• Use of force by a State against objects with no close association with another State. For non-State objects/targets that do not have a close association with a State, more will be required to bring the act within the scope of article 2(4), such as the presence of other factors including the gravity of the (potential) effects, a pre-existing dispute between States or a coercive intent against a State. The interplay of the various elements of a ‘use of force’ is discussed in more detail in Chapter 8.

It is controversial whether or under what circumstances the following uses of force by a State are in its ‘international relations’ and therefore fall within the scope of article 2(4):

• Use of force against entities falling short of Statehood.

• Use of force with no nexus to another State but against an international organisation or on terra nullius.

• Use of force within a State’s own territory against small-scale incursions by armed forces of another State.

• Use of force by a State in the exercise of its law enforcement jurisdiction against private foreign actors in the presence of additional factors. This is discussed further in Chapter 6.

Against the Territorial Integrity…

Despite the arguments by some scholars that these terms permit uses of force for a benign purpose,Footnote ⁶⁷ the second part of article 2(4) was introduced to ensure the prohibition was all-encompassing. This is made clear in the travaux préparatoires.Footnote ⁶⁸ For instance, at the San Francisco Conference, ‘[t]he Delegate of the United States made it clear that the intention of the authors of the original text was to state in the broadest terms an absolute all-inclusive prohibition; the phrase “or in any other manner” was designed to insure that there should be no loopholes’.Footnote ⁶⁹ This view was later confirmed during the drafting of the 1970 Friendly Relations Declaration. In the 1964 meeting of the Friendly Relations Special Committee, representatives who commented on the term ‘against the territorial integrity or political independence of any State’ said that this term

Furthermore, the notion of a permissible use of force for a benign purpose is not supported by State practice, was implicitly rejected by the ICJFootnote ⁷¹ and is overwhelmingly rejected by scholars.Footnote ⁷² Therefore, an otherwise prohibited use of force cannot be legally justified by arguing that it has a limited purpose.

Consent

This wording of article 2(4) does carve out an exclusion from the prohibition in the case of consent, which is not a circumstance precluding wrongfulness but forms an intrinsic part of the primary rule itself.Footnote ⁷³ According to the International Law Commission:

1970 Friendly Relations Declaration

The most important and comprehensive subsequent agreement of UN Member States on the interpretation of article 2(4) of the UN Charter is the Friendly Relations Declaration, which was adopted on 24 October 1970 by consensus by the UN General Assembly on the twenty-fifth anniversary of the United Nations. Principle 1 of the Declaration proclaims:

In the elaboration of this principle, UN Member States took a clear position on the interpretation of article 2(4) with respect to its scope of application to include the following: international boundaries, international lines of demarcation such as armistice lines;Footnote ¹⁶ forcible acts of reprisal;Footnote ¹⁷ using force to deprive peoples of the right to self-determination;Footnote ¹⁸ certain forms of interference in civil strife or terrorist acts in another StateFootnote ¹⁹ and military occupation or territorial acquisition resulting from the threat or use of force.Footnote ²⁰ (Paragraph 8 of Principle 1 of the Friendly Relations Declaration refers to ‘organizing or encouraging the organization of irregular forces or armed bands, including mercenaries, for incursion into the territory of another State’, however unlike other paragraphs listed under Principle 1, it does not link the legality of this action to a threat or use of force.Footnote ²¹ Indirect force is discussed in more detail later.) In addition to comprising subsequent agreement of UN Member States on the interpretation of article 2(4), the ICJ relied on the Friendly Relations Declaration in the Nicaragua case as an indication of States’ opinio juris on the existence and content of the customary prohibition of the use of forceFootnote ²² due to its references to ‘all States’,Footnote ²³ ‘principle’,Footnote ²⁴ ‘States’, ‘every State’,Footnote ²⁵ ‘a violation of international law and the Charter’Footnote ²⁶ and the statement that ‘[t]he principles of the Charter which are embodied in this Declaration constitute basic principles of international law’.Footnote ²⁷

1974 Definition of Aggression

1974 GA Resolution 3314 annexing the Definition of Aggression was adopted by acclamation (consensus) and was the first time that the international community agreed on a definition of aggression.Footnote ²⁸ Despite the significance of the 1974 Definition of Aggression, one should be careful about characterising the 1974 Definition as a ‘subsequent agreement’ regarding the interpretation of article 2(4), since it is actually defining aggression as a guideline for the UN Security Council’s political determination. Thomas Bruha argues that because of the politically negotiated nature of the 1974 Definition and its constructive ambiguity, the Definition must be read as a whole and in its context. One cannot extract elements of the ‘definition’ without taking this into account (as Bruha argues the ICJ did in the Nicaragua case). But given the wording in the Definition itself, which refers to uses of force, and the relationship between use of force and aggression – the annex to 1974 GA Resolution 3314 itself notes that ‘aggression is the most serious and dangerous form of the illegal use of force’Footnote ²⁹ – it is sound to infer a shared agreement or understanding that those acts listed in the Definition constitute ‘use of force’ under article 2(4)).

1987 GA Resolution 42/22

1987 GA Resolution 42/22 (adopted by consensus) was a Declaration on the Enhancement of the Effectiveness of the Principle of Refraining from the Threat or Use of Force in International Relations. This resolution reflects provisions of the 1970 Friendly Relations Declaration regarding non-intervention.Footnote ³⁰ Like the Friendly Relations Declaration, Resolution 42/22 confirms States’ view that the prohibition of the threat or use of force is universal and binding, referring to the prohibition as a ‘principle’,Footnote ³¹ holding that ‘[e]very State’ has the duty to comply with the prohibitionFootnote ³² and explicitly stating that ‘[t]he principle of refraining from the threat or use of force in international relations is universal in character and is binding, regardless of each State’s political, economic, social or cultural system or relations of alliance’.Footnote ³³

2005 World Summit Outcome Document

The 2005 World Summit at the United Nations Headquarters in New York was attended by over 170 Heads of State and Government. This summit produced and adopted by consensus the 2005 World Summit Outcome Document, which is historically and symbolically important as a united stand by UN Member States to reaffirm their commitment to the UN Charter and its purposes and principles in the face of modern challenges to the international order and human security. The principal importance of the 2005 World Summit Outcome Document for our purposes is that in it, the Member States of the UN ‘reaffirm that the relevant provisions of the Charter are sufficient to address the full range of threats to international peace and security’.Footnote ³⁴ This affirms States’ view of the continued relevance of the collective security framework of the UN Charter. The Outcome Document abridges the wording of article 2(4) in a way that makes it broader, by leaving out reference to ‘against the territorial integrity or political independence of any State’Footnote ³⁵ and replacing reference to ‘against the Purposes’ of the Charter with the threat or use of force ‘inconsistent with the Charter’.Footnote ³⁶ The document statesFootnote ³⁷ ‘[w]e rededicate ourselves to … refrain in our international relations from the threat or use of force in any manner inconsistent with the purposes and principles of the United Nations’. Although the earlier parts of the sentence which mention upholding the sovereign equality of States and respecting their territorial integrity and political independence could probably be said to implicitly cover the other parts of article 2(4), it is not clear what, if anything, this shows about the way that States interpret article 2(4).

Listed ‘Uses of Force’ in Subsequent Agreements

The aforementioned UN General Assembly resolutions passed by acclamation (consensus) show that UN Member States have taken a position regarding the interpretation of article 2(4) of the UN Charter with respect to its primary purposes and certain acts which fall within its scope. In particular, the 1970 Friendly Relations Declaration and the 1974 GA Definition of Aggression clearly demonstrate UN Member States’ subsequent agreement that the prohibition of the use of force in article 2(4) includes the following specific acts listed in those documents:

• The ‘use of force to violate the existing international boundaries of another State or as a means of solving international disputes, including territorial disputes and problems concerning frontiers of States’;Footnote ³⁸

• The ‘use of force to violate international lines of demarcation, such as armistice lines, established by or pursuant to an international agreement to which it is a party or which it is otherwise bound to respect’;Footnote ³⁹

• Forcible acts of reprisal;Footnote ⁴⁰

• ‘[A]ny forcible action which deprives peoples referred to in the elaboration of the principle of equal rights and self-determination of their right to self-determination and freedom and independence’;Footnote ⁴¹

• ‘[M]ilitary occupation resulting from the use of force in contravention of the provisions of the Charter’;Footnote ⁴²

• Acquisition of the territory of a State resulting from the threat or use of force;Footnote ⁴³

• ‘The invasion or attack by the armed forces of a State of the territory of another State, or any military occupation, however temporary, resulting from such invasion or attack, or any annexation by the use of force of the territory of another State or part thereof’;Footnote ⁴⁴

• ‘Bombardment by the armed forces of a State against the territory of another State or the use of any weapons by a State against the territory of another State’;Footnote ⁴⁵

• ‘The blockade of the ports or coasts of a State by the armed forces of another State’;Footnote ⁴⁶

• ‘An attack by the armed forces of a State on the land, sea or air forces, or marine and air fleets of another State’;Footnote ⁴⁷

• ‘The use of armed forces of one State which are within the territory of another State with the agreement of the receiving State, in contravention of the conditions provided for in the agreement or any extension of their presence in such territory beyond the termination of the agreement’.Footnote ⁴⁸

• The following forms of indirect uses of force are also prohibited:

  • ‘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.Footnote ⁴⁹

  • ‘The action of a State in allowing its territory, which it has placed at the disposal of another State, to be used by that other State for perpetrating an act of aggression against a third State’.Footnote ⁵⁰

The 1974 Definition of Aggression shows that UN Member States interpret the concept of ‘armed force’ quite broadly. However, these subsequent agreements of UN Member States leave unclear whether article 2(4) prohibits ‘armed’ force only, and what the elements of a prohibited ‘use of force’ are. As there are no statements in the travaux préparatoires that a special meaning of the term ‘use of force’ was intended by the parties under article 31(4) of the VCLT, Chapters 5 and 6 will now examine the ordinary meaning of this term.

Physical/Armed Force Only?

The role of article 2(4) in the UN collective security system and its primary objective of the maintenance of international peace and security supports interpreting the term ‘use of force’ as confined to armed/physical force only. This is because forms of non-physical coercion do not directly concern international peace and security but relate more to sovereign equality and the non-intervention principle. Some scholars such as Nikolas Stürchler have argued that the latter (i.e. freedom of choice for States) is not the primary concern of article 2(4). This understanding of article 2(4) excludes non-forcible forms of intervention from the scope of the prohibition of the use of force. This interpretation is further borne out by the following factors: firstly, the choice of the drafters to employ the term ‘use of force’ to overcome the problems associated with the term ‘war’; secondly, references to ‘force’ elsewhere in the UN Charter refer to ‘armed force’; and thirdly, that economic coercion was explicitly rejected by the drafters as a form of ‘force’ falling under article 2(4).

Regarding the choice of term ‘use of force’, as discussed earlier, the historical context of article 2(4) was intended to address the problems of the Covenant of the League of Nations and the Kellogg–Briand Pact, which used the restrictive notion of ‘war’.Footnote ⁵⁹ References to ‘armed force’ in the UN Charter further support this interpretation of force (referred to later). In particular, preambular paragraph 7 of the Charter refers to armed force, stating one of the goals of the Charter is ‘to ensure, by the acceptance of principles and the institution of methods, that armed force shall not be used, save in the common interest’. With respect to other forms of non-forcible coercion such as economic coercion, the proposal of the Brazilian delegate to the San Francisco conference to include ‘the threat or use of economic measures’ under article 2(4) was rejected by the drafting committee.Footnote ⁶⁰ The counter-argument, that the explicit reference to ‘armed force’ in other parts of the UN Charter might indicate that the absence of the qualifier ‘armed’ in article 2(4) shows that the drafters did not intend to restrict the term ‘force’ in this way, is less plausible if the latter provision is read in its historical context and in the light of the exclusion of economic coercion. It is then far more persuasive to hold that ‘force’ in article 2(4) only refers to armed force.

The question of whether article 2(4) extends to other forms of coercion was re-opened and subject to extensive debates in the drafting of the Friendly Relations Declaration, but there was ultimately no subsequent agreement overturning the drafter’s clear intent on this point. In each session of the Special Committee,Footnote ⁶¹ delegates debated this issue and could not reach agreement about the definition of ‘force’ in article 2(4) and, in particular, whether it included armed force only or also other forms of pressure threatening the territorial integrity or political independence of a State, such as economic coercion. Many (mostly newly independent and developing) States were in favour of a broad interpretation of ‘force’ to include not only armed force but also economic, political and other forms of pressure or coercion.Footnote ⁶² Several proposals included provisions to the effect that the term ‘force’ should be interpreted broadly to cover not only armed force but also economic, political and other forces of pressure,Footnote ⁶³ particularly those which ‘had the effect of undermining the territorial integrity or political independence of a State’.Footnote ⁶⁴ Some States in favour of a broad interpretation of the term ‘force’ beyond armed force were nevertheless cautious about including other forms of coercion within the concept ‘in order to avoid enlarging the scope of self-defence’.Footnote ⁶⁵

Textual arguments in favour of a broad interpretation of ‘force’ included the terms ‘in any other manner’ in article 2(4) of the UN Charter,Footnote ⁶⁶ and the fact that since other provisions of the UN Charter refer to ‘armed force’ (the Preamble and articles 41, 42, 43, 44 and 46) it is to be presumed that the drafters of the Charter did not intend to limit the term ‘force’ in article 2(4) in this way.Footnote ⁶⁷ The newly independent States emerging after the process of decolonisation noted that they had not had a chance to shape the interpretation of article 2(4) during the San Francisco Conference and argued that ‘economic and political forms of pressure were sometimes even more dangerous than armed force, particularly for developing countries’.Footnote ⁶⁸ ‘Many representatives emphasized the need to interpret the term “force” in the light of developments subsequent to the drafting of the Charter.’Footnote ⁶⁹ Reference was made to the fact that various international declarations, resolutions and treaties had included a broad understanding of ‘force’ and recognised the duty of States to refrain from undue pressure, including economic or other forms of pressure, such as the Bandung, Belgrade and Cairo Declarations, UN General Assembly Resolutions 2131 (xx) and 2160 (xxi), the Charter of the Organization of African Unity and article 51 VCLT and the Declaration on the Prohibition of Military, Political or Economic Coercion adopted by the Vienna Conference on the Law of Treaties.Footnote ⁷⁰

The third report of the Special Committee sums up ‘the arguments advanced during the debate in favour of a broad interpretation of the term “force” in formulating the principle of the prohibition of the threat or use of force’:

On the other hand, many States strongly maintained that ‘force’ within the meaning of article 2(4) was confined to armed force.Footnote ⁷² Delegates of these States opposed the inclusion of economic, political and other forms of coercion within the scope of article 2(4). The third report of the Special Committee sums up their arguments as follows:

It was also argued that ‘apart from basic legal objections to the inclusion of economic and political pressures in the definition of force, there was no legally satisfactory definition of economic and political pressures’.Footnote ⁷⁴

The Friendly Relations Declaration left open the issues of whether a prohibited use of force must be ‘armed’, and whether coercion falls within the scope of the prohibition. Although the Declaration was adopted by acclamation (consensus), seventy-nine delegations made statements on the formulation of the draft declaration at the time of its adoption,Footnote ⁷⁵ and the Rapporteur of the Sixth Committee, Mr Owada, noted that ‘the text of the declaration should be read in conjunction with the statements made for the record which are included in the relevant part of the summary records of the Sixth Committee, contained in documents A/C.6/SR.1178 to 1184’.Footnote ⁷⁶ The delegate for the UK, Sir Vincent Evants, drew

In particular, the delegate for Nigeria, Mr Shittabey, on behalf of the African Group of States expressed regret over ‘the Committee’s failure to accept the legitimate notion that the expression “force” as employed in the principle of the non-use of force denotes economic and political pressures as well as every kind of armed force’.Footnote ⁷⁸

In the text of the adopted Declaration, the prohibition of coercion is mentioned twice, firstly in the ninth preambular paragraph which ‘[r]ecall[s] the duty of States to refrain in their international relations from military, political, economic or any other form of coercion aimed against the political independence or territorial integrity of any State’ (emphasis added). The prohibition of coercion is also included with respect to the principle of the duty of non-intervention.Footnote ⁷⁹ However, the Special Committee reached no ultimate agreement on the issue of whether the prohibition of the use of force includes the prohibition of other forms of coercion.Footnote ⁸⁰ Some delegations expressed their understanding that ‘[t]he forms of coercion referred to in [preambular paragraph 9] were examples of unlawful forms of the threat or use of force, which was prohibited under the Charter’,Footnote ⁸¹ and others criticised the fact that ‘the principle concerning the prohibition of political, economic and other forms of coercion’ was ‘covered only in the preamble and not in the operative part’ and considered that it should have been placed in the principle concerning the non-use of force or in the general part of the declaration.Footnote ⁸²

Ultimately the lack of agreement regarding the definition of ‘force’ with respect to the principle of the non-use of force in the 1970 Friendly Relations Declaration was left unresolved. Accordingly, the 1970 Friendly Relations Declaration does not constitute a subsequent agreement regarding whether or not ‘force’ in article 2(4) refers to physical/armed force only.

Another potential subsequent agreement regarding whether ‘force’ in article 2(4) refers to armed/physical force only is the 1974 Definition of Aggression. Article 1 of the 1974 Definition provides that:

The introduction of the qualifier ‘armed’ before ‘force’ is the most significant difference to the text of article 2(4).Footnote ⁸⁴ On first glance, the use of the term ‘armed’ tends to bolster the view that article 2(4) of the UN Charter is directed at armed force only, since that article forms part of the collective security framework of the UN (which is also the context of the Definition of Aggression, for the purposes of providing guidance to the UN Security Council in making a determination under article 39 of the Charter). As discussed, the debates leading up to the Friendly Relations Declaration did not resolve the disagreements between States about whether article 2(4) was confined to armed force only, so the use of the qualifier ‘armed’ in article 1 of the Definition of Aggression could be viewed as a progressive development of international law through the subsequent agreement of the parties regarding the interpretation of article 2(4). Bruha argues that the use of this adjective ‘ended the discussion on “economic” or “ideological” aggression, which had lost much of its significance in the atmosphere of détente looming at that time’.Footnote ⁸⁵ However, since article 1 is defining aggression, the most serious form of illegal use of force, it does not follow that all illegal uses of force involve armed force. Hence, article 1 of the Definition of Aggression does not unequivocally indicate agreement of the UN Member States regarding the interpretation of article 2(4) as referring to armed force only.Footnote ⁸⁶

In absence of a subsequent agreement regarding the interpretation of ‘force’ in article 2(4), according to article 32 of the VCLT:

Accordingly, given the ambiguity of the text of article 2(4) regarding the meaning of ‘force’ and in the absence of a subsequent agreement regarding its interpretation, one should revert to the clear drafter’s intent expressed in San Francisco by the rejection of the Brazilian proposal to include economic coercion, that ‘force’ does not extend to other forms of non-armed/non-physical coercion. Despite some earlier scholarly views,Footnote ⁸⁷ the position that ‘force’ in article 2(4) includes only armed/physical force and excludes other forms of non-armed coercion is today overwhelmingly supported by scholars.Footnote ⁸⁸

Weapons

The ICJ has confirmed that article 2(4) does ‘not refer to specific weapons’; articles 2(4), 51 and 42 of the UN Charter ‘apply to any use of force regardless of the weapons employed’.Footnote ⁸⁹ The ICJ’s view has been affirmed by States in the comment to article 3(b) of the 1974 Definition of Aggression. Article 3(b) 1974 Definition of Aggression lists as an act of aggression: ‘Bombardment by the armed forces of a State against the territory of another State or the use of any weapons by a State against the territory of another State’ (emphasis added). The comment annotated to article 3(b) refers to paragraph 20 of the 1974 GA Special Committee report, which states: ‘the Special Committee agreed that the expression “any weapons” is used without making a distinction between conventional weapons, weapons of mass destruction and any other kind of weapon.’ This makes clear States’ agreement that at least with respect to aggression (and there is no apparent reason it should not extend to all illegal uses of force), the type of weapon used does not affect the lawfulness of the use of force under the jus contra bellum. Although explicitly referring to use of weapons, this term is broadly understood in the annotated comment of the Special Committee. It could also further be argued that as article 3(b) of the 1974 Definition refers to the most serious uses of force (i.e. aggression), it is not necessary that all uses of force (those below the threshold of an act of aggression) should require the employment of a weapon. In any event, the ICJ’s well-known statement does not explicitly state that a weapon must be employed for an act to fall under article 2(4) of the UN Charter, merely that no specific weapon is referred to by article 2(4) and that article 2(4) applies ‘to any use of force regardless of the weapons employed’. Although this does imply that some kind of weapon should be employed, it is not explicitly stated. Apparently, then, the type of weapon is not relevant to whether an act falls under the scope of article 2(4). But this still leaves the question: is the use of a weapon required at all for an act to fall under the prohibition of the use of force in article 2(4), and if so, what is a ‘weapon’?

Kinetic/Physical Means

‘Kinetic’ is defined as ‘[p]roducing or causing motion’.Footnote ⁹⁷ Although the scholarly literature often refers to ‘kinetic force’, it is more accurate to speak of kinetic energy and the transfer or release of kinetic energy to other objects. In conventional weapons, the transfer of kinetic energy occurs when, for example, a bullet that is discharged from a firearm strikes an object and transfers its kinetic energy to that object in the form of kinetic energy and heat, causing physical damage. Since the prohibition of the use of force in article 2(4) undoubtedly covers the use of chemical, biological and nuclear weapons,Footnote ⁹⁸ a kinetic release of energy is clearly not always required for an act to fall within the scope of the prohibition. Other examples that may fall under the category of forcible acts through employing means other than the release of kinetic energy may include cyber operations;Footnote ⁹⁹ certain types of interference with space systems such as ‘deliberate interference and “soft kill” techniques against satellites, such as laser dazzling and radio frequency jamming’Footnote ¹⁰⁰ or spoofing;Footnote ¹⁰¹ non-conventional weapons such as chemical, biological or nuclear weapons;Footnote ¹⁰² use of the environment as a weaponFootnote ¹⁰³ such as diverting a river or spreading fire across a border; and other measures such as contaminating a water source, releasing harmful substances into the air and expulsion of populations.Footnote ¹⁰⁴

Not all of these examples are necessarily ‘uses of force’ within the meaning of article 2(4); this is merely to illustrate the different means through which it is possible to create physical effects without the kinetic release of energy typically associated with a conventional weapon. One factor that may contribute to the characterisation of some of these non-‘kinetic’ means as a ‘use of force’ is indeed their effect. In sum, physical means are not essential for an act to be characterised as a ‘use of force’ within the meaning of article 2(4) but rather a certain physical effect. Henderson argues that ‘a consideration of the effects of the action takes on a greater importance the further one moves away from what we might consider to be conventional weapons’.Footnote ¹⁰⁵ This approach also coincides with the Tallinn Manual’s commentary on the definition of the use of force with respect to cyber operations, which sets out indicative factors for whether a cyber operation is a ‘use of force’, focusing on its effects rather than its means.Footnote ¹⁰⁶

Indirect Use of Force

In addition, with respect to means, the 1970 Friendly Relations Declaration and the 1974 GA Definition of Aggression clearly demonstrate UN Member States’ subsequent agreement that the prohibition of the use of force in article 2(4) includes the following forms of indirect uses of force: ‘The action of a State in allowing its territory, which it has placed at the disposal of another State, to be used by that other State for perpetrating an act of aggression against a third State’;Footnote ¹⁰⁷ ‘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’;Footnote ¹⁰⁸ and ‘organizing or encouraging the organization of irregular armed forces or armed bands, including mercenaries, for incursion into the territory of another State’.Footnote ¹⁰⁹ These refer to indirectness of means, rather than of effects, and are discussed further in Chapter 7 (anomalous examples of ‘use of force’).

Physical Harm to Persons or Objects

Although it is clear that a forcible act that directly results in physical harm to persons or property (and that meets the other requirements of article 2(4)) will be characterised as a ‘use of force’ under article 2(4),Footnote ² there is nothing explicit in the text of article 2(4) itself that restricts its scope to physical harm or harm to certain objects. A physical effect may not always be required for an act to constitute a prohibited ‘use of force’.Footnote ³ However, non-physical effects alone (such as psychological, economic or more abstract forms of harm) are not likely to be legally relevant to the determination of whether an act is a ‘use of force’. During the 1964 meeting of the Friendly Relations Special Committee, ‘[i]t was … pointed out that force could not be exercised in the abstract; when used, it was directed against an international legal entity, including its political organization, population and territory’.Footnote ⁴ More abstract forms of harm, such as breaking a diplomatic bagFootnote ⁵ or an unauthorised visit by a Head of State such as the visit by Turkish prime minister Ahmet Davutoglu to visit an Ottoman tomb within the Syrian border on 10 May 2015, which the Syrian government called ‘a clear aggression’,Footnote ⁶ are unlikely to be widely considered by States as a ‘use of force’ and will fall instead under other legal principles such as the principle of non-intervention.

Christian Henderson states, ‘[i]t may also be that humans are neither killed or injured, nor property damaged or destroyed, when the prohibition is engaged’.Footnote ⁷ This is due to the emphasis in article 2(4) on territorial integrity and political independence, which does not require harm to persons or property. This is a similar argument to that in Chapter 4 regarding the interpretation of ‘international relations’ and whether uses of force against objects with no nexus to another State fall within the scope of the prohibition. The object or target of the ‘use of force’ can therefore be relevant to both elements: whether the act is in ‘international relations’ and whether it is in fact a ‘use of force’. A forcible act that targets or causes damage to something other than a person or an object is likely to fall outside the scope of the prohibition on both counts.

Directness

The physical effect of a ‘use of force’ must be ‘sufficiently direct’.Footnote ⁸ The commentary to rule 69 in the Tallinn Manual 2.0 (which defines a ‘use of force’ with respect to cyber operations) suggests that the criterion of directness relates to States’ perception of the military nature of the act, since ‘[i]n armed actions … cause and effect are closely related’.Footnote ⁹ Directness here refers not to the time elapsed between the use of force and its effect (since in the case of nuclear weaponsFootnote ¹⁰ or cyber operationsFootnote ¹¹ for example, some of the most damaging effects may be delayed) but rather to proximity, that is, the lack of intermediate steps between the action and its result. This means that the use of force should be the proximate cause of harm. This would exclude non-physical ‘force’ such as cyber operations adversely affecting financial markets or the electricity grid. The potential problem with including such acts within the scope of article 2(4) is a lack of sufficient directness of the physical effects, rather than the effects themselves, since clearly interruptions to a power supply of, for instance, a nuclear power plant or a hospital can lead to physical harm to persons and property, or in the case of interruption of power supply or radio signals to a military facility, this could yield a military advantage to the attacking State.

Permanent and Temporary Effects

The text of article 2(4) does not reveal whether the effects of an act must be permanent for it to be characterised as a ‘use of force’. The Tallinn Manual 2.0 does not explicitly list permanence of effects as a criterion for characterising a cyber operation as a ‘use of force’, but the application of its listed criteria (severity, immediacy, directness, invasiveness, measurability of effects, military character, State involvement and presumptive legality) would implicitly include certain cyber operations with only temporary effects, for example, if there is a severe and immediate effect of a military character.Footnote ¹² Acts which do not cause permanent damage but which could potentially be regarded as a ‘use of force’ include cyber operations such as Denial of ServiceFootnote ¹³ and non-kinetic, non-cyber operations that interfere with satellites such as dazzling with lasers, electromagnetic interference for orbital jamming, terrestrial jamming, hijacking, spoofing or scanning.Footnote ¹⁴ For instance, Kazuto Suzuki notes that

It is not clear if these acts which cause temporary physical effects would be considered uses of force by States. For instance, in response to further GPS disruption by the DPRK in 2016, South Korea wrote to the UN Security Council that ‘[t]he GPS jamming by DPRK is an act of provocation that poses a threat to the security of the Republic of Korea’Footnote ¹⁶ but did not invoke the language of article 2(4) of the UN Charter or the right of self-defence under article 51. Uses of force which have only temporary effects are not excluded from a textual interpretation of article 2(4), but it remains to be seen whether subsequent practice of States will demonstrate their agreement regarding such an interpretation. Significant problems of attribution for these types of non-kinetic operations may complicate State’s response and legal characterisation of these acts.

It is interesting to consider whether acts with temporary effects would require a higher gravity threshold (or some other factor) to qualify as a prohibited use of force; in the aforementioned examples of cyber attacks and interference with satellites, it is the gravity (e.g. military nature) of the effects or of the potential effects (e.g. in the case of GPS disruption, potential aviation disasters) that is important rather than the actual direct (temporary) damage/disruption of function. With increasing reliance by States on satellite technology (for instance, the reliance of the United States on satellite technology with respect to its military presence and potential military operations in geographically distant theatres such as the South China SeaFootnote ¹⁷), it is entirely plausible that even acts with only a temporary effect of disabling or interfering with space systems may in future be treated by States as violating the prohibition of the use of force. Uses of force in outer space are further analysed and discussed in Chapter 8.

Actual or Potential Effects

The wording of article 2(4) of the UN Charter with respect to the threat or use of force is distinguished from article 51 regarding temporality. The phrase ‘if an armed attack occurs’ has been the subject of much controversy and debate as to whether it limits the right of self-defence to after an armed attack ‘occurs’.Footnote ¹⁸ However, article 2(4) does not mention effects or temporality at all (which is sensible, given that unlike article 51, it does not define conditions for the exercise of a right) but only refers to the terms ‘threat’ and ‘use’ of force. It is therefore textually ambiguous whether any physical effect (i.e. harm) must actually ensue for such acts to fall within the scope of the prohibition of the use of force, or if it is sufficient if there is a potential for physical effects/harm to result.

State practice is mixed and insufficient to draw a definite conclusion regarding whether potential harmful effects would suffice to constitute a prohibited ‘use of force’ under article 2(4). There are some notable examples of merely potential effects being treated as a ‘use of force’ and even an ‘armed attack’, such as the attempted assassination of former US President George Bush in Kuwait in 1993 (discussed in Chapter 8).Footnote ¹⁹ But of recent alleged State-sponsored assassinations and attempted assassinations involving the use of radioactive (Litvinenko) or chemical weapons (Skripal – analysed in greater detail in Chapter 8, and the assassination of Kim Jong-nam allegedly by North Korean agents in Malaysia on 13 February 2017 with XV nerve agent), article 2(4) was only invoked in relation to the Skripal incident and by only one State (the UK).Footnote ²⁰ It is therefore unclear if potential effects would suffice to meet the requirements of article 2(4).

It may be that acts with merely potential effects would only meet the threshold of a ‘use of force’ under article 2(4) if they occur in combination with other elements, such as a higher gravity of the potential effects, a clear hostile or coercive intention, or a particularly close connection between another State and the object/target of the act. These considerations may relate to the element of ‘international relations’, since the targeted (attempted) killing of an individual may rise to the level of an international incident due to the use of a prohibited weapon with serious potential effects for the population of the territorial State (as was the case in the attempted assassination of Sergei Skripal with the prohibited nerve agent Novichok). The notion of a combined threshold of elements for an act to constitute a ‘use of force’ and the relationship between the elements of a ‘use of force’ and contextual elements such as ‘international relations’ is explored in more detail in Part III.

Conclusion

It is clear that forcible acts with direct (i.e. sufficiently proximate) physical effects on persons or objects may constitute a ‘use of force’ and fall within the scope of the prohibition of the use of force in article 2(4) if the other requirements of that provision are met. It is textually unclear and remains to be seen through the subsequent practice of States if forcible acts with only temporary effects would fall within the scope of the prohibition in article 2(4). It is similarly legally uncertain if forcible acts with potential but unrealised effects would suffice to constitute a prohibited ‘use of force’ under article 2(4). It is likely that other elements of a ‘use of force’ will be decisive for determining whether such acts meet the definition of this term. The rest of this chapter will consider if there is a requirement for a particular gravity or intention for a prohibited ‘use of force’.

Conclusion

Ultimately, the controversy regarding the gravity threshold of a ‘use of force’ under article 2(4) is not solved by the text of that provision, which neither specifies nor excludes a gravity threshold for an act to constitute a ‘use of force’ and therefore fall within the scope of the prohibition. Accordingly, the matter is uncertain at the legal of textual interpretation. The issue of whether article 2(4) has a de minimis gravity threshold depends on the subsequent practice of States in their application of this provision. The analysis of subsequent practice by other scholars in relation to this issue, especially by Corten and Ruys, demonstrates that the interpretation of this practice and the conclusion of whether a ‘use of force’ has a gravity threshold is strongly influenced by the position one takes regarding the legal significance of silence and inaction. This author finds Ruys’ analysis of State practice on this matter convincing and agrees that there is no de minimis gravity threshold as such for a prohibited ‘use of force’ under article 2(4). However, this section has argued that gravity is nonetheless a relevant factor to an assessment of whether an act violates article 2(4) on two bases: firstly, as a factor relevant to whether the act occurs in ‘international relations’ (e.g. as an indicator of intention), and, secondly, as a relevant factor to whether the act constitutes a ‘use of force’ for acts that may otherwise not meet the threshold of the definition, for instance, because its effects are temporary or only potential. The complex relationship between ‘international relations’ and of gravity and intention as elements of a ‘use of force’ is illustrated in further detail in Part III.

Intention and ‘Threat … of Force’

The meaning of prohibited threats of force in article 2(4), similar to its counterpart of prohibited force, has received relatively little treatment in scholarshipFootnote ⁵⁴ and jurisprudence.Footnote ⁵⁵ The ICJ’s jurisprudence does not make clear whether coercion is required for an unlawful ‘threat of force’. The Corfu Channel case could be interpreted this way, since in that case the ICJ held that the UK was entitled to make threats if the purpose was to deter Albania from firing on its ships, but it was not entitled to make a demonstration of force ‘for the purpose of exercising political pressure’ on Albania.Footnote ⁵⁶ However, this case is of little precedential value in determining the meaning of article 2(4), because it is so ambiguous and has been cited in support of diametrically opposed positions.Footnote ⁵⁷

The two main scholars who have examined the meaning of threats of force in article 2(4), Nikolas StürchlerFootnote ⁵⁸ and Romana Sadurska, have different views on whether coercion is a necessary element of prohibited threats. Stürchler argues that coercion is not an essential element of a prohibited ‘threat of force’. Despite article 2(7) of the Charter, which guarantees States freedom of choice, the primary purpose of the UN Charter is the prevention of war rather than freedom of choice (i.e. freedom from coercion).Footnote ⁵⁹ He gives the example of a war-mongering State that is no longer trying to ensure compliance with anything – a threat or use of force by that State is thus not coercive (no compliance is sought), but it is still unlawful.Footnote ⁶⁰ But coercion could still be a ‘strong indicator’Footnote ⁶¹ in determining the unlawfulness of threats under article 2(4), in which case what distinguishes unlawful threats from unlawful intervention is the ‘military dimension’.Footnote ⁶² The relevance of coercion as a criterion is in showing ‘that the threat of force is not, when properly understood, the mere preparation for the use of force.’Footnote ⁶³ Rather, threats can be ends in themselves by ensuring compliance at a much lower cost than an actual use of force. Sadurska agrees that the prohibition of threats of force is aimed at international security rather than the individual liberty of each State from external pressureFootnote ⁶⁴ but takes as her starting point a concept of threat of force as ‘a form of coercion because it aims at the deliberate and drastic restriction or suppression by one actor of the choices of another’.Footnote ⁶⁵ Hence, it is uncertain whether coercion constitutes an essential ingredient of a prohibited threat of force, although, at the very least, it may be considered a strong indicator of unlawfulness.

Intention and ‘Use of Force’

There is a similar lack of consensus among scholars focusing on the meaning of ‘use of force’ as to whether intention is an element of a prohibited ‘use of force’. Ian Brownlie argues that intention is not part of the criteria of prohibited use of force and believes this is a good thing, because to hold otherwise would create unacceptable loopholes in the prohibition.Footnote ⁷⁸ In contrast to Brownlie, Corten argues that ‘[s]uch an intention appears to be an essential characteristic of the use of force under the Charter’.Footnote ⁷⁹ Henderson also argues that ‘it is clear that there must be an intention to use force, or an animus belligerandi, in order to breach the prohibition of the threat or use of force’.Footnote ⁸⁰ Ruys notes that ‘state practice reveals that, when faced with territorial incursions ostensibly or allegedly lacking hostile intent, territorial states often refrain from invoking the language of Article 2(4) or 51’.Footnote ⁸¹ However, he notes that this does not necessarily reflect a legal conviction and that State responsibility is ‘objective’ so does not require intent unless this forms part of the primary rule.Footnote ⁸² For small-scale incursions, Ruys states that ‘the key is to determine whether they reflect a hostile intent’ to exclude unintentional or harmless acts.Footnote ⁸³ With respect to law enforcement within a State’s own territory, Ruys argues that manifest hostile intent is sufficient but not necessary for an act to be a ‘use of force’.Footnote ⁸⁴

Adding to the lack of clarity is that the scholarly literature is not consistent in the use of this term. A hostile intention may refer to an intended action, intended effects or intended coercion. The difference is significant, because it may capture or exclude different categories of forcible acts. To speak of a mental state of an abstract entity such as a State is a fiction, since States have neither a physical body nor mind and can only act indirectly through individuals. Therefore, a mental element attaching to a State obligation (in this case, to refrain from the ‘use of force’ under article 2(4) of the UN Charter) would be satisfied if it is held by a person whose conduct is attributable to the State under the rules set out in the ILC Articles on State Responsibility relating to attribution.Footnote ⁸⁵ This could be either the individual using force (e.g. a soldier) or directing the use of force (a military commander or government official). With respect to what is meant by a hostile intention, at the very least, it requires ‘that the State in question is aware it is undertaking an action against another State’.Footnote ⁸⁶

Conclusion

Ultimately, whether or not intention is required for a prohibited use of force under article 2(4) cannot be definitively resolved at the level of textual analysis. It is possible that hostile intent is an indicative factor that can turn a forcible act that would otherwise not meet various criteria, such as gravity or if the harm is only potential but unrealised, into a ‘use of force’. This discussion about the interrelationship between different elements of a ‘use of force’ (including the relationship between intention, gravity and international relations with respect to maritime law enforcement versus ‘use of force’) is continued in Part III.