International Law and the Preemptive Use of Force Against Iraq

CRS Report for Congress
International Law and the Preemptive Use of
Force Against Iraq
David M. Ackerman
Legislative Attorney
American Law Division
On March 19, 2003, the United States, aided by Great Britain and Australia,
initiated a military invasion of Iraq. Both the U.S. and Great Britain contended that
they had sufficient legal authority to use force against Iraq pursuant to Security Council
resolutions adopted in 1990 and 1991. But President Bush also contended that, given
the “nature and type of threat posed by Iraq,” the U.S. had a legal right to use force “in
the exercise of its inherent right of self defense, recognized in Article 51 of the UN
Charter.” Given that the U.S. had not previously been attacked by Iraq, that contention
raised questions about the permissible scope of the preemptive use of force under
international law. This report examines that issue as it has developed in customary
international law and under the United Nations Charter. It will be updated as events
warrant. (For historical information on the preemptive use of force by the U.S., see CRS
Report RS21311, U.S. Use of Preemptive Military Force.)
Preemptive Military Attacks Under Customary International Law
Until recent decades customary international law deemed the right to use force and
even to go to war to be an essential attribute of every state. As one scholar summarized:
It always lies within the power of a State to endeavor to obtain redress for wrongs, or
to gain political or other advantages over another, not merely by the employment of1
force, but also by direct recourse to war.
Within that framework customary international law also consistently recognized self-
defense as a legitimate basis for the use of force:
An act of self-defense is that form of self-protection which is directed against an
aggressor or contemplated aggressor. No act can be so described which is not

1 Hyde, Charles Cheney, International Law Chiefly As Interpreted and Applied by the United
States, Vol. 3 (1945), at 1686.
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occasioned by attack or fear of attack. When acts of self-preservation on the part of
a State are strictly acts of self-defense, they are permitted by the law of nations, and
are justified on principle, even though they may conflict with the ... rights of other2
Moreover, the recognized right of a state to use force for purposes of self-defense
traditionally included the preemptive use of force, i.e., the use of force in anticipation of
an attack. Hugo Grotius, the father of international law, stated in the seventeenth century3
that “[i]t be lawful to kill him who is preparing to kill.” Emmerich de Vattel a century
later similarly asserted:
The safest plan is to prevent evil, where that is possible. A Nation has the right to
resist the injury another seeks to inflict upon it, and to use force ... against the
aggressor. It may even anticipate the other’s design, being careful, however, not to
act upon vague and doubtful suspicions, lest it should run the risk of becoming itself4
the aggressor.
The classic formulation of the right of preemptive attack was given by Secretary of
State Daniel Webster in connection with the famous Caroline incident. In 1837 British
troops under the cover of night attacked and sank an American ship, the Caroline, in U.S.
waters because the ship was being used to provide supplies to insurrectionists against
British rule in Canada headquartered on an island on the Canadian side of the Niagara
River. The U.S. immediately protested this “extraordinary outrage” and demanded an
apology and reparations. The dispute dragged on for several years before the British
conceded that they ought to have immediately offered “some explanation and apology.”
But in the course of the diplomatic exchanges Secretary of State Daniel Webster
articulated the two conditions essential to the legitimacy of the preemptive use of force
under customary international law. In one note he asserted that an intrusion into the
territory of another state can be justified as an act of self-defense only in those “cases in
which the necessity of that self-defense is instant, overwhelming, and leaving no choice5
of means and no moment for deliberation.” In another note he asserted that the force
used in such circumstances has to be proportional to the threat:
It will be for [Her Majesty’s Government] to show, also, that the local authorities of
Canada, even supposing the necessity of the moment authorized them to enter the
territories of the United States at all, did nothing unreasonable or excessive; since the
act, justified by the necessity of self-defence, must be limited by that necessity, and6

kept clearly within it.
2 Id. Vol. 1, at 237.
3 Grotius, Hugo, The Law of War and Peace, at 1625.
4 de Vattel, Emmerich, The Law of Nations, Vol. IV, at 3.
5 Letter from Secretary of State Daniel Webster to Lord Ashburton of August 6, 1842, set forth
in Moore, John Bassett, A Digest of International Law, Vol. II (1906), at 412.
6 Letter from Mr. Webster to Mr. Fox of April 24, 1841, 29 British and Foreign State Papers

1129, 1138 (1857), quoted in Damrosch, Lori, International Law: Cases and Materials (2001),

at 923.

Both elements – necessity and proportionality – have been deemed essential to legitimate
the preemptive use of force in customary international law.7
Effect of the United Nations Charter
However, with the founding of the United Nations, the right of individual states to
use force was purportedly curbed. The Charter of the UN states in its Preamble that the
UN was established “to save succeeding generations from the scourge of war”; and its
substantive provisions obligate Member States of the UN to “settle their international
disputes by peaceful means” (Article 2(3)) and to “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 manner inconsistent with the Purposes of the United Nations” (Article
2(4)). In place of the traditional right of states to use force, the Charter creates a system
of collective security in which the Security Council is authorized to “determine the
existence of any threat to the peace, breach of the peace, or act of aggression” and to
“decide what measures shall be taken ... to maintain international peace and security”
(Article 39).
Although nominally outlawing most uses of force in international relations by
individual States, the UN Charter does recognize a right of nations to use force for the
purpose of self-defense. Article 51 of the Charter provides:
Nothing in the present Charter shall impair the inherent right of individual or
collective self-defence if an armed attack occurs against a Member of the United
Nations, until the Security Council has taken measures necessary to maintain8
international peace and security.
The exact scope of this right of self-defense, however, has been the subject of ongoing
debate. Read literally, Article 51’s articulation of the right seems to preclude the
preemptive use of force by individual states or groupings of states and to reserve such
uses of force exclusively to the Security Council. Measures in self-defense, in this9

understanding, are legitimate only after an armed attack has already occurred.
7 In its advisory opinion on the Legality of the Threat or Use of Nuclear Weapons, the
International Court of Justice stated that “[t]he submission of the exercise of the right of self-
defence to the conditions of necessity and proportionality is a rule of customary international
law.” 1996 I.C.J. Reports para. 41.
8 United Nations Charter, Article 51.
9 This reading of Article 51 finds support in the decision of the International Court of Justice in
Military and Paramilitary Activities in and Against Nicaragua (Nicaragua v. United States of
America), 1986 I.C.J. Reports p. 14. The gravamen of the Court’s ruling was that in customary
international law as well as Article 51, the use of force in self-defense is justified only in
response to an armed attack:
... [F]or one State to use force against another ... is regarded as lawful, by way of
exception, only when the wrongful act provoking the response was an armed attack
.... In the view of the Court, under international law in force today – whether
customary international law or that of the United Nations system – States do not have
a right of “collective” armed response to acts which do not constitute an “armed

Others contend that Article 51 should not be construed so narrowly and that “it
would be a travesty of the purposes of the Charter to compel a defending state to allow
its assailant to deliver the first, and perhaps fatal, blow ....”10 To read Article 51 literally,
it is said, “is to protect the aggressor’s right to the first strike.”11 Consequently, to avoid
this result, some assert that Article 51 recognizes the “inherent right of individual or
collective self-defence” as it developed in customary international law prior to adoption
of the Charter and preserves it intact. The reference to that right not being impaired “if
an armed attack occurs against a Member of the United Nations,” it is said, merely
emphasizes one important situation where that right may be exercised but does not
exclude or exhaust other possibilities.12
In further support of this view, it is argued that the literal construction of Article 51
simply ignores the reality that the Cold War and other political considerations have often
paralyzed the Security Council and that, in practice, states have continued to use force
preemptively at times in the UN era and the international community has continued to
evaluate the legitimacy of those uses under Article 51 by the traditional constraints of
necessity and proportionality. The following examples illustrate several aspects of these
!In 1962 President Kennedy, in response to photographic evidence that the
Soviet Union was installing medium range missiles in Cuba capable of
hitting the United State, imposed a naval “quarantine” on Cuba in order
“to interdict ... the delivery of offensive weapons and associated
material.”13 Although President Kennedy said that the purpose of the
quarantine was “to defend the security of the United States,” the U.S. did
not rely on the legal concept of self-defense either as articulated in
Article 51 or otherwise as a justification for its actions. Abram Chayes,
the Legal Adviser to the State Department at that time, later explained the
decision not to rely on that justification as follows:

9 (...continued)
Id. para. 211.
10 Statement by Sir Humphrey Waldock, quoted in Roberts, Guy, “The Counterproliferation Self-
Help Paradigm: A Legal Regime for Enforcing the Norm Prohibiting the Proliferation of
Weapons of Mass Destruction,” 27 Denver Journal of International Law and Policy 483, 513
11 Id.
12 Simma, Bruno, ed., The Charter of the United Nations: A Commentary (1994), at 51. This
contention finds some support in the advisory opinion of the International Court of Justice in
Legality of the Threat or Use of Nuclear Weapons, 1996 I.C.J. Reports para. 96-97. In passing
on the question of whether it might ever be legal for a nation to use nuclear weapons, the Court
refused to construe Article 51 or customary international law to preclude “the use of nuclear
weapons by a State in an extreme circumstance of self-defence, in which its very survival would
be at stake. The Court’s decision did not specifically deal with the question of preemptive
attack. But it seems to give support to an expansive understanding of what might be permissible
in instances of extreme necessity.
13 Proclamation 3504, 27 Fed. Reg. 10401 (October 25, 1962).

In retrospect ... I think the central difficulty with the Article 51 argument
was that it seemed to trivialize the whole effort at legal justification. No
doubt the phrase “armed attack” must be construed broadly enough to
permit some anticipatory response. But it is a very different matter to
expand it to include threatening deployments or demonstrations that do not
have imminent attack as their purpose or probable outcome. To accept that
reading is to make the occasion for forceful response essentially a question
for unilateral national decision that would not only be formally
unreviewable, but not subject to intelligent criticism, either .... Whenever
a nation believed that interests, which in the heat and pressure of a crisis
it is prepared to characterize as vital, were threatened, its use of force in
response would become permissible .... In this sense, I believe that an
Article 51 defence would have signalled that the United States did not take
the legal issues involved very seriously, that in its view the situation was14
to be governed by national discretion, not international law.
!In 1967 Israel launched a preemptive attack on Egypt and other Arab
states after President Nasser had moved his army across the Sinai toward
Israel, forced the UN to withdraw its peacekeeping force from the Sinai
border, and closed the port of Aqaba to Israeli shipping, and after Syria,
Iraq, Jordan, and Saudi Arabia all began moving troops to the borders of
Israel. In six days it routed Egypt and its Arab allies and had occupied
the Sinai Peninsula, the West Bank, and the Gaza Strip. Israel claimed
its attack was defensive in nature and necessary to forestall an Arab
invasion. Both the Security Council and the General Assembly rejected
proposals to condemn Israel for its “aggressive” actions.15
!On June 7, 1981, Israel bombed and destroyed a nuclear reactor under
construction in Iraq. Asserting that Iraq considered itself to be in a state
of war with Israel, that it had participated in the three wars with Israel in
1948, 1967, and 1973, that it continued to deny that Israel has a right to
exist, and that its nuclear program was for the purpose of developing
weapons capable of destroying Israel, Israel claimed that “in removing
this terrible nuclear threat to its existence, Israel was only exercising its
legitimate right of self-defense within the meaning of this term in
international law and as preserved also under the United Nations
Charter.”16 Nonetheless, the Security Council unanimously
“condemn[ed] the military attack by Israel in clear violation of the
Charter of the United Nations and the norms of international conduct”
and urged the payment of “appropriate redress.”17

14 See Chayes, A., The Cuban Missile Crisis (1974), at 63-64, quoted in Carter, Barry, and
Trimble, Phillip, International Law (1999), at 1241-42.
15 The Security Council, instead, adopted Resolution 242 calling on Israel to withdraw from the
territories and for the termination of all claims or states of belligerency and the acknowledgment
of the territorial integrity and the right of every State in the region to live in peace.
16 20 ILM 996 (July, 1981) (excerpts from Security Council debate).
17 Id. at 993 (S/RES/487 adopted on June 19, 1981).

Current Situation
Thus, in both theory and practice the preemptive use of force appears to have a home
in current international law. Its clearest legal foundation is in Chapter VII of the UN
Charter. Under Article 39 the Security Council has the authority to determine the
existence not only of breaches of the peace or acts of aggression that have already
occurred but also of threats to the peace; and under Article 42 it has the authority to “take
such action by air, sea, or land forces as may be necessary to maintain or restore
international peace and security.” These authorities clearly seem to encompass the
possibility of the preemptive use of force. Less clear is whether international law
currently allows the preemptive use of force by a nation or group of nations without
Security Council authorization. That would seem to be permissible only if Article 51 is
read not literally but as preserving the use of force in self-defense as traditionally allowed
in customary international law. As noted, the construction of Article 51 remains a matter
of debate. But so construed, Article 51 would not preclude the preemptive use of force
by the U.S. against Iraq or other sovereign nations. To be lawful, however, such uses of
force would need to meet the traditional requirements of necessity and proportionality.
As the examples listed above illustrate, the requirement of necessity is most easily
met when an armed attack is clearly imminent, as in the case of the Arab-Israeli War of
1967. But beyond such obvious situations, as Abram Chayes argued, the judgment of
necessity becomes increasingly subjective; and there is at present no consensus either in
theory or practice about whether the possession or development of weapons of mass
destruction (WMD) by a rogue state justifies the preemptive use of force. Most analysts
recognize that if overwhelmingly lethal weaponry is possessed by a nation willing to use
that weaponry directly or through surrogates (such as terrorists), some kind of anticipatory
self-defense may be a matter of national survival; and many – including the Bush
Administration – contend that international law ought to allow, if it does not already do
so, for the preemptive use of force in that situation.18 But many states and analysts are
decidedly reluctant to legitimate the preemptive use of force against threats that are only
potential and not actual on the grounds the justification can easily be abused. Moreover,
it remains a fact that the international community judged Israel’s destruction of Iraq’s
nuclear reactor site in 1981 to be an aggressive act rather than an act of self-defense.
Iraq has become an occasion to revisit the issue. Iraq had not attacked the U.S., nor
did it appear to pose an imminent threat of attack in traditional military terms. As a
consequence, it seems doubtful that the use of force against Iraq could be deemed to meet
the traditional legal tests justifying preemptive attack. But Iraq may have possessed
WMD, and it may have had ties to terrorist groups that seek to use such weapons against
the U.S. If evidence is forthcoming on both of those issues, then the situation necessarily
raises the question that the Bush Administration articulated in its national security
strategy, i.e., whether the traditional law of preemption ought to be recast in light of the
realities of WMD, rogue states, and terrorism. Iraq likely will not resolve that question,
but it is an occasion to crystallize the debate.

18 The Bush Administration contends that “we must adapt the concept of imminent threat to the
capabilities and objectives of ... rogue states and terrorists.” See White House, The National
Security Strategy of the United States of America (Sept. 2002), at 15.