Aggression

• Author: Craig Forcese/Leah West
• Pages: 117-144

117

CHA PTER 4

AG GR ESSION

Historically, the greatest threat to the state has been agg ression by

another state. Aggression entails the loss of territory and population

and potentially the conquest and di ssolution of the state. Since at least

1928, and the Kellogg-Briand Pact,1 wars of conquest have been unlaw-

ful, a prohibition armed and reinforced by the UN Charter. Article

2(4) of the UN Charter specif‌ies that “all Members shall refrain in their

international relat ions from the threat or use of force against the ter-

ritorial integr ity or political independence of any state, or in any other

manner inconsistent with the Purposes of t he United Nations.”2 The

rule also exi sts as part of customar y international law3 and is w idely

regarded as a jus cogens norm — that is, a “peremptory” legal rule that

cannot be set aside by treat y.4 Wars resulting in territorial aggrandize-

ment are, therefore, now illegal and, in practice, very unusual.

1 General Treaty for the Renuncia tion of War as an Instrument of Natio nal Policy, 94

League of Nationa l Treaty Series 5 7.

2 Charter of the United Nat ions, Can TS No 7 (1945) (“UN Charter ”).

3 Nicaragua v United States of Amer ica, [1986] ICJ Rep 14 at para 187 et seq [Nicar-

agua Case].

4 A jus cogen s, or peremptory, norm “is a norm accepted a nd recognized by

the intern ational community of States a s a whole as a norm from which no

derogation is per mitted and which can be modi f‌ied only by a subsequent norm

of general inter national law having t he same character.” Vienna Convention on

the Law of Treaties, 1155 UNTS 331, Art 53. See discussion in Hele n Duy, The

“War on Terror” and the Framework of Internat ional Law (Cambridge: Cambridge

University Pre ss, 2005) at 147.

NATIONAL SECUR ITY LAW118

Still, states (and increasi ngly, non-state actors) use force regularly in

international relat ions, and unlaw ful uses of force may imperil a state’s

national securit y interests. States direct much of their i ntelligence

collection at anticipating the means a nd intent of foreign militaries,

organized armed g roups, and their leaders. Whatever other functions

it performs, the Canad ian Armed Forces (CAF), and the militaries of

like-minded countries, ex ist to deter and, if necessary, repel aggression

by other states — a defensive function accepted by international l aw.

We discuss foreign and defence intelligence collection in Chapters 9

and 10 and provide an overview of the rules govern ing how the CAF

may use force in Chapter 17. In this chapter, we outline the legal stan-

dards prohibiting the ag gressive use of force in international l aw, as

well as those rules entitling a response to it. This chapter is about, in

other words, when st ates may use force in international l aw.

PART I: LIMITATIONS ON USE OF FORCE

Jus ad bellum is the body of international rules determini ng when

recourse to militar y force is permissible.5 As noted, Art icle 2(4) of

the UN Charter (and its customary equivalent) lies at the core of the

modern international law on the use of force. It bars all states “from

the threat or use of force against the ter ritorial integrity or political

independence of any state, or in any other manner inconsi stent with

the Purpose s of the United Nations.”

This prohibition is broad. Certain jur ists urge that a use of force

might fall short of impairi ng the “territorial integr ity or political

independence of any state” and, therefore, would not be prohibited.6

However, in practice it is dicult to imagine any non-consensual use

of force involving states that does not in some way impair a st ate’s ter-

ritorial integr ity or political independence. For instance, the very act

5 The discussion in t his section is parti ally adopted from Craig Forcese & L eah

West, “Killing C itizens: Core Legal Dilem mas in the Targeted Killi ng of Can-

adian Terroris t Fighters Abroad” (2017) 54 Canadia n Yearbook of Inter national

Law 134.

6 The narrow interpretat ion of Art 2(4) is sometime s raised to justify “hum anitar-

ian interve ntion.” See di scussion, for example, in Celest e Poltak, “Hu manitar-

ian Interve ntion: A Contemporary Inter pretation of the Charter of the Unite d

Nations” (2002) 60:2 University of Toronto Faculty of Law Revie w 1. Humanitar-

ian interve ntion is discussed f urther below.