The Use of Force

• Author: John H. Currie; Craig Forcese; Joanna Harrington; Valerie Oosterveld
• Pages: 805-860

805

CHAPTER 14

The Use of Force

A. INTRODU CTION

In this chapter, we consider the extent to which international law permits states to use mil-

itary force against one another (and in some situations against non-state actors). We dis-

cuss this as a matter of international law enforcement because the circumstances in which

states may lawfully use force have eectively been narrowed to those in which the target has

breached certain of its international legal obligations.

This is not to suggest, however, that the use of force is generally available as a response to

the violation by a state of any of its international legal obligations. As previously noted in Chap-

ter , modern international law as a general rule outlaws resort to force by states against other

states, subject only to certain narrowly dened exceptions. We therefore begin with a review of

the scope of the general prohibition of the use of force in interstate relations, followed by an

examination of the limited exceptions to that general prohibition. We will see that the excep-

tions amount to necessary means — when all other options have been exhausted or are other-

wise unavailable — of securing respect for certain fundamental international legal obligations.

B. THE GENERAL PROHIBITION OF THE THREAT OR USE OF FORCE

As seen in earlier chapters, Article () of the Charter of the United Nations sets out a basic

prohibition: “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.” The corollary obligation is

found in Article () of the UN Charter: “All Members shall settle their international disputes

by peaceful means.” Given the terse wording of the principle set out in Article (), the Gen-

eral Assembly decided to elaborate on its meaning in the  Friendly Relations Declaration:

Declaration on Principles of International Law Concerning Friendly Relations and Co-operation in

accordance with the Charter of the United Nations, GA Res  (XXV), UN Doc A/RES//

XXV, reprinted in UN GAOR, th Sess, Supp No  at –, UN Doc A/ Corr  ();

()  ILM 

The principle that States shall refrain in their inter national relations from the threat or use

of force against the territorial integrit y or political independence of any State, or in any other

manner inconsistent with the purposes of the United Nations:

 Charter of the United Nations,  June , Can TS  No , in force  October  [UN Charter].

806 INTERNATIONAL LAW: DOCTRINE, PRACTICE, AND THEORY

Every State has the duty to refrain in its 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. Such a threat or use

of force constitutes a violation of international law and the Charter of the United Nations

and shall never be employed as a means of settling international issues.

A war of aggression constitutes a crime against the peace, for which there is respons-

ibility under international law.

In accordance with the purposes and principles of the United Nations, States have

the duty to refrain from propaganda for wars of aggression.

Every State has the duty to refrain from the threat or 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. . . .

States have a duty to refrain from acts of reprisal involving the use of force.

Every State has the duty to refrain from any 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.

Every State has the duty to refrain from organizing or encouraging the organization

of irregular forces or armed bands, including mercenaries, for incursion into the terri-

tory of another State.

Every State has the duty to refrain from organizing, instigating, assisting or partici-

pating in acts of civil strife or terrorist acts in another State or acquiescing in organized

activities within its territory directed towards the commission of such acts, when the ac ts

referred to in the present paragraph involve a threat or use of force.

The territory of a State shall not be the object of military occupation resulting from

the use of force in contravention of the provisions of the Charter. The territory of a State

shall not be the object of acquisition by another State resulting from the threat or use of

force. No territorial acquisition resulting from the threat or use of force shall be recog-

nized as legal. Nothing in the foregoing shall be construed as aecting:

(a) Provisions of the Charter or any international agreement prior to the Charter regime

and valid under international law; or

(b) The powers of the Security Council under the Charter. . . .

Nothing in the foregoing paragraphs shall be construed as enlarging or diminishing

in any way the scope of the provisions of the Charter concerning cases in which the use

of force is lawful.

While not a formal source of international law in its own right, the Friendly Relations

Declaration (also referred to as General Assembly Resolution  (XXV)) was adopted by

consensus and is generally accepted to be an expression of customary international law. Con-

sider the signicance accorded to its provisions by the International Court of Justice (ICJ) in

the course of its discussion of the scope and nature of the prohibition of the use of force in

the following case:

Military and Paramilitary Activities in and against Nicaragua (Nicaragua v United States of America),

Merits, Judgment, [] ICJ Rep 

[Nicaragua claimed that the United States had used force unlawfully against it, contrary

to Article () of the UN Charter. The following excerpts of the case set out the Court’s

reasoning on this issue.]

Chapt er : The Use of Force 807

. The Court . . . nds that both Parties take the view that the principles as to the

use of force incorporated in the United Nations Charter correspond, in essentials, to

those found in customary international law. The Parties thus both take the view that the

fundamental principle in this area is expressed in the terms employed in Article , para-

graph , of the United Nations Charter. . . . The Court has however to be satised that

there exists in customary international law an opinio juris as to the binding character of

such [a principle]. This opinio juris may, though with all due caution, be deduced from,

inter alia, the attitude of the Parties and the attitude of States towards certain General

Assembly resolutions, and particularly resolution  (XXV). . . . The eect of consent

to the text of such resolutions cannot be understood as merely that of a “reiteration or

elucidation” of the treaty commitment undertaken in the Charter. On the contrary, it may

be understood as an acceptance of the validity of the rule or set of rules declared by the

resolution by themselves. The principle of non-use of force, for example, may thus be

regarded as a principle of customary international law. . . .

. A further conrmation of the validity as customary international law of the

principle of the prohibition of the use of force expressed in Article , paragraph , of the

Charter of the United Nations may be found in the fact that it is frequently referred to

in statements by State representatives as being not only a principle of customary inter-

national law but also a fundamental or cardinal principle of such law. The International

Law Commission, in the course of its work on the codication of the law of treaties,

expressed the view that “the law of the Charter concerning the prohibition of the use of

force in itself constitutes a conspicuous example of a rule in international law having the

character of jus cogens” (paragraph () of the commentary of the Commission to Article

 of its draft Articles on the Law of Treaties, ILC Yearbook, -II, p. ). Nicaragua

. . . in the present case states that the principle prohibiting the use of force embodied in

Article , paragraph , of the Charter of the United Nations “has come to be recognized

as jus cogens”. The United States . . . found it material to quote the views of scholars that

this principle is a “universal norm”, a “universal international law”, a “universally recog-

nized principle of international law”, and a “principle of jus cogens”. . . .

. The Court will appraise the facts in the light of the principle of the non-use of

force . . . . What is unlawful, in accordance with that principle, is recourse to either the

threat or the use of force against the territorial integrity or political independence of any

State. For the most part, the complaints by Nicaragua are of the actual use of force against

it by the United States. Of the acts which the Court has found imputable to the Govern-

ment of the United States, the following are relevant in this respect:

– the laying of mines in Nicaraguan internal or territorial waters in early  . . . ;

– certain attacks on Nicaraguan ports, oil installations and a naval base. . . .

These activities constitute infringements of the principle of the prohibition of the use

of force, dened earlier, unless they are justied by circumstances which exclude their

unlawfulness, a question now to be examined. The Court has also found . . . the exist-

ence of military manoeuvres held by the United States near the Nicaraguan borders; and

Nicaragua has made some suggestion that this constituted a “threat of force”, which is

equally forbidden by the principle of non-use of force. The Court is however not satised

that the manoeuvres complained of, in the circumstances in which they were held, con-

stituted on the part of the United States a breach, as against Nicaragua, of the principle

forbidding recourse to the threat or use of force.

. Nicaragua has also claimed that the United States has violated Article , para-

graph , of the Charter, and has used force against Nicaragua in breach of its obligation