Use of Force

1. LWN158:
Public International Law
SEMINAR WEEK 6
JUS AD BELLUM

2. Objectives this week
 To critically examine the international legal norms governing
the use of force including:
 The prohibition on the use of force contained in art 2(4)
of the UN Charter;
 The right to self-defence, including individual and
collective self-defence, anticipatory and pre-emptive self-
defence;
 Collective security under Ch VII of the UN Charter (see
also week 9).
 To consider the implications of other possible justifications
for the use of force, including the doctrines of responsibility
to protect and humanitarian intervention.

3. Disambiguation
 International law includes two areas relating to the use of
force:
1. Jus ad bellum – laws relating to the commencement of
armed conflict
2. Jus in bello – laws relating to the conduct of armed conflict
(or international humanitarian law)
 This week: jus ad bellum
 Next week: jus in bello

4. United Nations Charter:
Prohibition on the Threat or Use of Force
 UN Charter article 2(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.”
 Article 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.”

5. Customary prohibition on use of force
 Nicaragua (Merits) decision confirms that the prohibition in article
2(4) is binding on all states as a matter of customary international
law
 Also confirmed principle of non-intervention in the domestic affairs
of other states
 Based on principles of sovereign equality of all states (in article
2(1)) and territorial sovereignty (Corfu Channel (Merits))
 Principle of non-intervention includes both armed and non-armed
activities
 Where an intervention involves use of force it will breach both
articles 2(1) and 2(4).

6. What is ‘use of force’?
 Definition comes from Declaration on Principles of International Law
Concerning Friendly Relations and Cooperation Among States in
Accordance with the United Nations Charter (General Assembly
Resolution 2625, 24 October 1970)
 Declaration expands on the prohibition contained in art 2(4) and sets out
a number of specific duties which States have, including duties to refrain
from:
 propaganda for wars of aggression
 threat or use of force to violate existing boundaries of another State or as
means of solving international disputes
 threat or use of force to violate international lines of demarcation, such
as armistice lines
 acts of reprisal involving use of force
 forcible action which deprives people of right to self-determination,
freedom and independence

7. Declaration on Friendly Relations:
 organising or encouraging the organisation of irregular forces or armed
bands, including mercenaries, for incursion into the territory of other
States
 organising, instigating, assisting or participating in acts of civil strife or
terrorist acts in another State, or acquiescing in organised activities
within its territory directed towards the commission of such acts, where
they involve threat or use of force
 Declaration also specifies that wars of aggression constitute crime
against peace to which international responsibility attaches (but
‘aggression’ not defined)
 Resolution expressly avoids ‘enlarging or diminishing in any way the
scope of the provisions of the Charter concerning cases in which the use
of force is lawful’

8. Aggression
 Some uses of force will be aggression
 Declaration on Friendly Relations: ‘aggression’ = crime against peace, but not
defined
 Resolution on the Definition of Aggression (GA Resolution 3314 of 14
December 1974):
 “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”

9. Declaration on the Definition of
Aggression
 Art 3: lists certain acts said to qualify as acts of aggression.
(a) Invasion or attack by armed forces on territory of another State, or military
occupation, or annexation of territory
(b) Bombardment or use of weapons against territory of another State
(c) Blockade of ports or coasts of another State
(e) Use of armed forces which are by arrangement within the territory of another
State in a manner inconsistent with the terms of that arrangement
(f) Allowing territory to be used by another State to perpetrate act of aggression
against a third State
(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.

10. Definition of Aggression cont/...
 Art 4: SC may determine other acts to constitute aggression
(list is not exhaustive)
 Acts listed in art 3 have been recognised as reflecting
customary international law (Nicaragua (Merits) case
 A State will not be able to evade legal responsibility for
aggression by using armed bands, mercenaries, irregulars
or terrorists with no formal link to the State, provided the
State has ‘sent’ them or has been ‘substantially involved’ in
their sending.

11. Definition of Aggression in the Rome
Statute
 Art 8 bis: “For the purpose of this Statute, ‘crime of
aggression’ means the planning, preparation,
initiation or execution, by a person in a position
effectively to exercise control over or to direct the
political or military action of a State, of an act of
aggression which, by its character, gravity and scale,
constitutes a manifest violation of the Charter of
the United Nations.”

12. Aggression and the Rome Statute of
the International Criminal Court
 Art 5: ICC has jurisdiction over the crime of aggression
 Rome Statute entered into force in 2002 but
jurisdiction over aggression was not to commence until
parties had agreed on definition of crime
 2010: first Review Conference for parties to Rome
Statute in Kampala, Uganda
 Adopted article 8 bis: definition of aggression
 Court won’t be able to exercise jurisdiction over the
crime until after 1 January 2017, when states are to
make a decision on activation of jurisdiction.

13. Two views on UN Charter Art 2(4)
 Prohibits 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.”
 Two possible interpretations:
1. Narrow view: Only prohibits use of force where intended to affect
territorial integrity or political independence – so might not include force
used to address gross violations of human rights
2. Broad view: Completely prohibits use of force unless a specific exception
can be found in Charter, on the basis that a complete view of Statehood
requires that any use of force would be against territorial integrity.
 Second view has more support from UN and state practice – that is,
use of force is unlawful unless it falls within one of the specific
exceptions.

14. Exceptions to the prohibition on the
use of force
Two exceptions in UN Charter
1. Self-defence
2. Collective measures authorised by the Security Council under Chapter
VII
And also possible customary exceptions:
3. Invitation by state
4. Protection of nationals abroad
5. Humanitarian intervention
6. Responsibility to protect

15. Self-defence: UN Charter art 51
“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 the Security
Council has taken measures necessary to maintain international
peace and security. Measures taken by Members in the exercise
of this right of self-defence shall be immediately reported to the
Security Council and shall not in any way affect the authority and
responsibility of the Security Council under the present Charter
to take at any time such action as it deems necessary in order to
maintain or restore international peace and security.”

16. An inherent right to self-defence
 Art 51: “inherent right” – so not created by UN Charter but
existing right
 What is position under customary international law?
 The Caroline (1837) – test for lawful self-defence:
 There must be a necessity of self-defence which is both instant and
overwhelming
 There must be no choice of means
 There must be no moment for deliberation
 Force used in self-defence must not be unreasonable or excessive

17. Inherent right to self-defence cont/...
 Nicaragua (Merits) case: confirmed right of self-defence in
customary international law but must be:
1. proportionate to attack, and
2. necessary to respond to it.
No mention of requirement for no choice of means or moment for
deliberation.
 Nuclear Weapons Advisory Opinion: confirmed customary
law requirements of necessity and proportionality (split
decision)

18. Art 51: “Armed attack”
 Article 51 preserves right of self defence if an armed attack occurs.
 What constitutes an ‘armed attack’?
 Nicaragua (Merits):
 not merely any action by regular armed forces across an international
border
 Includes sending armed bands, groups, irregulars, mercenaries by a State to
carry out acts of armed force of such gravity as to amount to actual armed
conduct
 Or substantial involvement therein
 Based on definition of ‘aggression’ in article 3(g) of GA Res 3314, which the
court considered to be reflective of customary international law

19. “Armed attack” cont/...
 Nicaragua (Merits): introduces test of ‘scale and effects’: in order for an
act of aggression to equate to an armed attack sufficient to justify self-
defence, it must be on a scale and produce effects greater than a mere
frontier incident
 Sending by a State of armed bands to the territory of another State could
be an armed attack, but merely providing weapons or other support would
not be
 But court noted that providing such support could be an unlawful threat or
use of force, or an unlawful intervention in the internal affairs of another
state, it just wouldn’t be an ‘armed attack’ sufficient to justify self-defence.
 So: not every use of force = ‘armed attack’ which would trigger right to self-
defence
 But an accumulation of events may amount to an armed attack, even
where each event on its own would be inadequate (Oil Platforms case)

20. Attribution of Armed Attacks
 Nicaragua (Merits): Right to self-defence does not arise where armed
attack is carried out by groups whose conduct is not attributable to a
state.
 Confirmed in Armed Activities in the Congo decision – no evidence that
use of force by rebels was attributable to the Congo.
 Attacks by non-state actors (eg terrorists) can trigger right to self-
defence where there is sufficient evidence that sovereign state is
providing support or tolerating activities (see Security Council
resolutions following 9/11).

21. Anticipatory self-defence?
 Art 51: “if an armed attack occurs”
 Does this mean that a State can’t resort to force in self-defence unless
an armed attack has actually commenced against them, even where
there is strong evidence of an imminent attack?
 Advantage of strict approach:
 certainty that attack has occurred;
 clarity and transparency regarding motives of defending state
 Disadvantages:
 strengthens the hand of an aggressor;
 denies advantage of pre-emptive strike.

22. Anticipatory self-defence and the
Caroline principle
 Customary self-defence as set out in the Caroline doesn’t include words ‘if an
armed attack occurs’ – instead allows self-defence where the need is ‘instant
and overwhelming’.
 This has been argued to support a right of anticipatory self-defence, allowing a
state to act where threat of armed attack is imminent
 Anticipatory self-defence would still be limited by principles of necessity and
proportionality
 This approach seems to be ruled out by language of art 51 which limits self-
defence to situations where armed attack has occurred, BUT article 51 says that
nothing interferes with the ‘inherent’ right to self defence.
 So: is the ‘inherent’ right the same as the Caroline concept of anticipatory self-
defence?

23. Anticipatory self-defence cont/…
 Nicaragua: the ICJ didn’t rule specifically on lawfulness of response to imminent
attack, but did confirm that existence of an ‘armed attack’ is a prerequisite for
self-defence – other threat to national interests not involving an armed attack
would not be sufficient.
 Still doubt whether an anticipatory use of force in response to an imminent
armed attack would be lawful.
 Some have argued that customary position now is more narrow than Caroline
principle
 Brownlie: contemporary state practice has rejected the flexible approach in Caroline
 Henkin: limited to actual armed attack – no anticipatory right exists
 Triggs: adopting a broad definition of ‘armed attack’ might remove the need to rely on
anticipatory right – would include situation where attack is ‘genuinely imminent’
 Other scholars: no sense requiring state to wait for attack to occur if they know
it’s inevitable

24. Anticipatory self-defence cont/…
 If anticipatory self-defence is lawful, there must be an ‘imminent’ attack
 Distinguish ‘pre-emptive’ self-defence, which would allow action before
attack is imminent.
 Concept of ‘imminent attack’ implies that attack is inevitable
 Usually understood in context of traditional military action – where
preparations for war are readily observable
 Can be more difficult to establish for more modern forms of force
 Cyber attacks?
 Terrorist attacks?
 Might need to refer to pattern of past attacks to establish imminence
 Support for pre-emptive right is more controversial – see Bush Doctrine and
justification for invasion of Iraq in 2003 (weapons of mass destruction)

25. Anticipatory self-defence cont/…
 If anticipatory self-defence is permitted, it must still be
necessary and proportionate
 This can be problematic, as it’s difficult to establish what a
necessary or proportionate response is to an attack which
hasn’t yet occurred
 This is even more difficult with a pre-emptive use of self-
defence, as the armed attack is even more remote and
uncertain

26. Collective self-defence
 Art 51: individual or collective self-defence
 When can a State use force in defence of another State which claims to have been
attacked?
 An act of collective self-defence must meet all requirements of individual self-
defence:
 An armed attack
 Proportionality
 Necessity
 Observance of humanitarian law
 Additionally, the victim State must have requested the assistance of the third State
(Nicaragua (Merits) case)
 Recent action in Syria against IS is example of collective self-defence, requested by
Iraq.

27. Second exception: Security Council
Authorisation of Use of Force (Ch VII)
 A State may use force against another State if it has received
prior authorisation from the Security Council, which has
primary responsibility for the maintenance of international
peace and security (Art 24(1))
 Art 39: Security Council shall determine existence of any
threat to peace, breach of peace or act of aggression and
make recommendations
 Art 41: Security Council shall decide what measures not
involving the use of armed force are to be employed to give
effect to its decisions.

28. Article 42: authorisation of the use of
force
“Should the Security Council consider the measures provided for in
Article 41 would be inadequate or have proved to be inadequate,
it may take such action by air, sea or land forces as may be
necessary to maintain or restore international peace and security.
Such action may include demonstrations, blockade, and other
operations by air, sea or land forces of Members of the United
Nations.”
Article 43: Members of the UN undertake to provide armed forces and
other assistance to maintain international peace and security

29. Other exceptions: Invitation by State
 Where use of force is carried out with the consent or
invitation of the State concerned it will not be a violation of
article 2(4).
 Example: Regional Assistance Mission to the Solomon Islands
(RAMSI)
 Solomon Islands requested assistance from other States to provide
internal security and stability in the face of breakdown of internal law
and order
 Forces provided by Australia, NZ, Fiji, PNG, Samoa & Tonga

30. Other exceptions: Protections of
Nationals Abroad
 State practice supports limited right to use force against another
state to protect nationals – has been argued as justification by some
states but remains controversial (eg in Tehran Hostages case)
 Rationale is that use of force to protect nationals is an extension of
the right to self-defence.
 Should first attempt to get State in whose territory they are located
to intervene. Where that State is unwilling or unable to protect
them, should try to obtain its permission to intervene
 Should seek assistance of UN where that would be adequate, but if
UN not able to act in time and need for instant action is manifest,
could use force, provided it was limited to securing safe removal of
nationals and was not used as a pretext for other force or action.

31. Protection of nationals abroad
cont/...
 Use of force would still need to be necessary and
proportionate.
 Huber J in Spanish Zones of Morocco: right to intervene might
exist, but presupposes that other means of protection are
inadequate
 US Diplomatic and Consular Staff in Tehran Case (US v Iran)
(Tehran Hostages) : ICJ didn’t rule explicitly on the legality of
the operation but did comment that intervention is ‘of a kind
calculated to undermine respect for the judicial process in
international relations’ – suggests that ICJ is likely to view
intervention to protect nationals as unacceptable except as a
last resort.

32. Possible exception: Humanitarian
Intervention
 Controversial doctrine which posits that use of force may
be justified where it is necessary to address overwhelming
human catastrophe, even without Security Council
approval.
 No right exists in international law, either in treaty or
custom – strictly speaking would be violation of art 2(4)
 But some scholars (and some states) have argued that an
exception ought to be made in order to address situations
where use of force is necessary but Security Council has
failed to act – strict conformity with the law can’t be
justified in the face of human catastrophe.

33. Humanitarian intervention cont/...
 No clear ruling from ICJ on legal status of humanitarian
intervention but some dicta:
 Nicaragua and Tehran Hostages: ICJ commented that protection of
human rights in those cases was incompatible with the use of force
which actually occurred – couldn’t justify use of force on
humanitarian grounds
 Accepting a right of humanitarian intervention would also be a
dangerous precedent – would risk abuse by powerful states
 Suggests that even if right did exist, use of force would still have to
be necessary and proportionate.
 Legality of the Use of Force case – intervention in Kosovo: ICJ unable
to decide the legal issues because it had no jurisdiction to hear
claims by Serbia and Montenegro.

34. Responsibility to Protect
 “Collective international responsibility to protect which is exercisable by the SC
authorising military force as a last resort in situations of genocide, ethnic
cleansing, or serious violations of humanitarian law which the state has proved
powerless or unwilling to prevent.”
 Rationale is that a State has a responsibility to protect its citizens but where a
state fails to protect, the responsibility should fall to the international
community
 Usually considered to be limited to mass atrocities like war crimes, CAH and
genocide.
 Military force could be used if peaceful means have failed.
 Still requires approval by the Security Council :
 operates more as reconceptualisation of Ch VII powers than separate exception to
article 2(4).
 Intended to shift the way States feel about Ch VII mechanisms and when they should
be used