Pre-emptive action

October 10, 2005 - nr.36



  1. The debate that prompted the government to ask the AIV to produce a report was triggered by the publication of the US National Security Strategy in 2002. This report does not attempt to provide an exhaustive commentary on the Strategy. Rather, it only examines those aspects that are relevant to the questions put by the government. It should be pointed out, by the way, that the Strategy is not a legal document, but a political paper of a topical nature that does not offer strict guidelines for every conceivable scenario. The way the Strategy is used will gradually evolve in the light of new developments. These developments include the international political debate to which the present report is intended to contribute. Makers of security policy inevitably run up against the conflict between ‘regulation’ and ‘security’. States have an obligation to safeguard the security of their citizens. It goes without saying that the means they use to achieve this end should be effective. At the same time, however, such means should be consistent with the law. Both these aspects are of vital importance in the light of the ‘new threats’ to international peace and security. While states need to have access to effective means of protecting themselves, they also need an effective legal order that is capable, generally speaking, of constraining the action taken by states. The authors have sought to take account of this dichotomy in compiling this report.



  2. The report begins by analysing the terms ‘preventive’ and ‘pre-emptive’ military action. We then go on to outline the nature of the new threats and the US security doctrine, which is based on the concept of military action. The doctrine does not distinguish between pre-emptive and preventive action. We subsequently seek to assess whether such action is permissible under international law in that it satisfies the criteria for exceptions to the prohibition on the use of force set out in Article 2, paragraph 4, of the UN Charter. Those exceptions are the use of force by or on behalf of the Security Council and the right of self-defence.


    As far as the right of self-defence is concerned, we first examine Article 51 of the UN Charter, which grants states the right of self-defence in the event of an armed attack. We then consider whether ‘anticipatory self-defence’ or pre-emptive military action can be justified by placing a broader interpretation on the concept of an ‘armed attack’. We do this by examining such action in the light of the Caroline criteria (i.e. an instant, overwhel¬ming threat, leaving no choice of means and no moment for deliberation) and by examining state practice since 1945. We conclude that state practice is limited and unclear, as a result of which it is difficult to draw firm conclusions as to whether the Caroline criteria still apply under current international law.

    We nonetheless believe that the Caroline criteria are a useful tool for determining when Article 51 may be invoked in response to ‘new threats’ that cannot be countered in any other way (i.e. terrorism either on its own or in combination with the proliferation of weapons of mass destruction). In the event of an instant, overwhelming threat that leaves no choice of means and no moment for deliberation, the use of force could be acceptable as a means of anticipatory self-defence, provided that the criteria are strictly applied and that the principle of proportionality is observed.

  3. We conclude, however, that the US National Security Strategy is intended not only to prevent imminent threats (i.e. to pave the way for pre-emptive action), but also to prevent emerging threats from materialising (i.e. preventive action). We also conclude that the Strategy calls for the use of military force in such cases, and does not appear to envisage the development of any policy by the UN Security Council. This means that the US National Security Strategy can be justified only on the grounds of the second exception to the prohibition on the use of force, i.e. self-defence. As the US document does not contain any criteria that might be used to restrict the type of military action described in it, apart from the proviso that such action may not be used as a pretext for aggression, we conclude that the US National Security Strategy, in so far as it goes beyond the Caroline criteria, is not consistent with international law. The US National Security Strategy also appears to be inconsistent with the principle that the only body entitled to determine the existence of a threat to international peace and security under Article 39 of the Charter is the Security Council and that, accordingly, it is the Security Council which is obliged to take the necessary action.

  4. After analysing the permissibility of preventive military action under international law, we then go on to examine the international political context of the campaign against new threats (and developments within this context). In our view, the fact that international law as it currently stands does not permit preventive military action without a mandate from the Security Council should form a guiding principle for the Dutch government in its efforts to accomplish its constitutional mission of promoting the development of the international rule of law (under Article 90 of the Dutch Constitution).


    In this section, we make a number of suggestions for strengthening the system of collective security, the primary objective of which is to make the Security Council more effective. In addition, we point out the scope provided by the Charter for making greater use of the UN General Assembly, although we readily admit that little actual use has been made of this scope to date.

    Apart from strengthening the system of collective security, we believe that other, nonmilitary preventive measures, such as improvements in early-warning systems, poverty reduction and the promotion of good governance and human rights, can help to counter the new threats. We have also made proposals for strengthening international instruments intended specifically for countering the new threats, although we stress the need to make a clear distinction between the issues of weapons of mass destruction and terrorism.

    Finally, we also examined the political or military desirability of or need for preventive military action in a situation in which the Security Council fails to act even though it might reasonably have been expected to do so, and decision-making in the Council is either delayed or undermined for political reasons.

    We do not feel that it would be desirable - in anticipation of a possible situation in which the Security Council fails to act - to devise a set of criteria for an emergency of this type that would make military action either acceptable or even desirable. In the event of an emergency of this nature, the only way of safeguarding against arbitrariness is by insisting on the broadest possible consensus, for example the largest possible majority in the Security Council - at the very least a formal majority - disregarding the permanent members’ right of veto. Even a large majority in the General Assembly could, if the need arose, increase the political acceptability of action not authorised by the Security Council. The priority is still, however, to use all the means offered by the Charter to prevent this type of emergency.

Advice request

Professor K.C. Wellens
Chairman of the Advisory Committee on Issues of
Public International Law

Mr F. Korthals Altes
Chairman of the Advisory Council on
International Affairs
Postbus 20061
2500 EB Den Haag

The Hague
30 June 2003

Dear Professor Wellens and Mr Korthals Altes,

In its letter to the House of Representatives of 15 November 2002 (28600 V, no. 12), the government set out its position on the new American security strategy. The letter also discusses the concept of pre-emptive action which is a prominent feature of that strategy. During the debate on the Ministry of Foreign Affairs’ budget on 4 December 2002, in answer to a question from Mr Van Aartsen, I promised the House of Representatives to prepare a follow-up memorandum on the subject of ‘pre-emption’.

In that light, I believe it would be desirable to receive advice on a number of points. Since the subject covers both political issues and issues of public international law, it makes sense to address the question both to the Advisory Council on International Affairs (AIV) and the Advisory Committee on Issues of Public International Law (CAVV). The Minister of Defence and I would like to have your views on the following.

The aforementioned letter outlining the government’s position on the new National Security Strategy of the United States is enclosed. Chapter 3 of the American strategy paper deals with new threats and pre-emptive action. Since 11 September 2001 in particular, but before that date also, the American administration has insisted on its right to ‘act pre-emptively’ under certain circumstances against terrorists and ‘rogue states’ that have attempted, or are attempting, to acquire weapons of mass destruction. In its 1999 security strategy, the previous American administration already considered proportional, pre-emptive action against an ‘imminent threat’ to be justified in the case of a significant threat to national security. In the light of new threats said not to be ‘deterrable’, the current security strategy puts greater emphasis on that option. The US approach continues to seek the support of the international community, but, if necessary, the United States will exercise its right to self-defence and, in last resort, take unilateral pre-emptive action against terrorists and ‘rogue states’. To justify its position, the administration underscores the fact that, under recognised international law, ‘nations need not suffer an attack before they can lawfully take action to defend themselves against forces that represent an imminent danger of attack.’

The government’s opinion of the American security strategy is that the debate over the concept of ‘immediate threat’ must focus squarely on the central issue of what political and legal conditions any military response must satisfy. It is important to have a more detailed definition of the reasons for such action and a better explanation of proportionality and the grounds for justification. Measures to ensure that the concept is not misused are also necessary.

When discussing ‘pre-emptive action’, the issues of non-proliferation and the extent to which existing instruments are sufficient are important. The new American security analysis sees non-proliferation and pre-emptive action as closely related. The AIV’s advisory reports Developments in the international security situation in the 1990s: from unsafe security to insecure safety of September 1999 and An Analysis of the US Missile Defence Plans: pros and cons of striving for invulnerability of August 2002 have already dealt with the dangers of proliferation of weapons of mass destruction. The norms set out in arms control and disarmament treaties are extremely important but they can never eliminate proliferation completely. What is needed for disarmament is not so much new initiatives but an answer to the questions of how to enforce compliance to prevent the treaties from being eroded and how to deal with violators. In general, there must be more consideration of the ‘harder’ aspects of non-proliferation policy.

The government would ask the AIV/CAVV for an advisory report on the following.

  1. How do the AIV/CAVV understand the concept ‘pre-emptive action’?
  2. Could the AIV/CAVV indicate what conditions and circumstances can make pre-emptive action (within the meaning of the answer to question 1) politically/militarily desirable or necessary and/or acceptable under international law? Should criteria be established - and if so, which ones - in respect of the concept of threat (type, scope, immediacy, verifiability) and, in this connection, what is the relevance of the concept of proportionality?
  3. What guarantees must be in place or what review framework created to prevent or limit politically/militarily undesirable pre-emptive action, or pre-emptive action which contravenes public international law?

Yours sincerely,

Jaap de Hoop Scheffer
Minister of Foreign Affairs

Government reactions

To the President of the
House of Representatives
Binnenhof 22
Den Haag

Security Policy Department
Bezuidenhoutseweg 67
Postbus 20061
2500 EB Den Haag

Date        29 October 2004
Re.        AIV/CAVV advisory report on "Pre-emptive action"

On 30 June 2003 the government asked the Advisory Council on International Affairs (AIV) and the Advisory Committee on Issues of Public International Law (CAVV) to produce an advisory report on the acceptability of pre-emptive action in the light of new threats, including terrorism, the proliferation of weapons of mass destruction or a possible combination of the two.

The report was commissioned mainly in response to the US National Security Strategy, particularly the concept of pre-emptive action which it sets out. The government examined this strategy in a letter to the House of 15 November 2002 (Parliamentary Papers, House of Representatives, 28600 V, no. 12). That letter is appended to the advisory report. During the debate on the Foreign Affairs budget on 4 December 2002 my predecessor undertook to produce a follow-up memorandum on the issue of pre-emption. The AIV and CAVV were asked to provide advice and recommendations for the purposes of that memorandum. The Minister of Defence and I hereby submit to you the government's response to the conclusions in the advisory report Pre-emptive Action of July 2004, which was presented to the House on 14 September 2004 (ref. no. buza040290).

Pre-emptive action

The report defines pre-emptive action as military action taken against 'an imminent attack' (p. 5). In this, it sticks closely to the American thinking on pre-emption, which is based on the concept of imminent threat. In its 1999 security strategy the Clinton administration stated that it regarded proportional, pre-emptive action against an imminent threat as justified in the event of a serious threat to national security. This is reiterated in similar wording in the 2002 security strategy (particularly on p. 15), where the focus is again on the imminent threat concept.

In the view of the government, to clarify the terms of the discussion, it is highly important to draw a clear distinction between pre-emptive action and preventive action. As will be seen below, in the case of 'new' threats, under certain conditions, pre-emptive action may be taken against an imminent threat under Article 51 of the UN Charter.

Preventive action involves measures that can be taken when a threat is not imminent, including but not confined to the use of force. In this context one might consider a range of measures, from preventive diplomacy and development cooperation to sanctions and the use of the military, described as 'preventive engagement' in the European Security Strategy. Preventive action involving the use of force cannot be based on Article 51 of the Charter and is therefore only permitted on the authorisation of the Security Council. Preventive action in all its dimensions is an entirely different issue from pre-emptive action, and it will not be examined any further in this letter. The government's response focuses on pre-emptive action, which is referred to in the US security strategy and in the questions put to the AIV and CAVV.

UN Charter

Article 2, paragraph 4 of the Charter of the United Nations sets out a clear prohibition on the use of force. There are only two possible exceptions: use of force by or on behalf of the Security Council and use of force for the purposes of individual or collective self-defence (under Article 51). Article 51 is concerned with self-defence against an armed attack. It does not refer to the threat of an armed attack. The AIV/CAVV is however of the opinion that, in the case of new threats (terrorism, whether or not associated with the proliferation of weapons of mass destruction) which cannot be dealt with in any other way, Article 51 of the Charter could be invoked, albeit under strict conditions, in the event of an 'instant, overwhelming threat, leaving no choice of means, and no moment for deliberation' (p. 21). These are the so-called Caroline criteria for establishing whether it can be regarded as permissible under international law to invoke the right of self-defence in the face of an imminent attack. The report states, on p. 18, that the immediacy of the threat is central to the Caroline doctrine. As stated above, the US security strategy also takes 'imminent threat' as the basis for pre-emptive action.

The government agrees with the report's main conclusion that, when under threat of attack by terrorists and/or with weapons of mass destruction, under certain conditions a country may invoke the right of self-defence as contained in Article 51 of the UN Charter. No state can, after all, be asked or expected to do nothing in the face of clear indications that an attack by terrorists and/or weapons of mass destruction on its territory or population is imminent.

In the view of the government, too, there must be an 'imminent threat'. In order to be able to assess whether the right of self-defence has been lawfully invoked, we therefore need to address the question of when a threat qualifies as 'imminent'. The AIV/CAVV conclude that the Caroline criteria are a suitable tool for answering that question. They are no more and no less than a tool, however, because at the same time the report states that it is difficult to draw the firm conclusion, on the basis of state practice, that the Caroline criteria still apply under current international law (p. 21).

The Caroline doctrine

The government observes that in the international debate on pre-emptive action, more and more frequent reference is made to the Caroline criteria. At the same time, the government agrees with the AIV/CAVV that state practice is 'limited and unclear', as stated on p. 21 of the report. In principle, the government shares the AIV/CAVV's view that the criteria are a suitable tool for assessing whether Article 51 can be invoked. However, it questions whether, particularly in the case of new threats, the criteria are entirely adequate and wonders whether they may not have to be further refined at some point. One example would be the threat of a digital attack on computer networks essential to a country's security. Although this might not constitute a traditional armed attack within the meaning of Article 51 of the UN Charter (since it would involve no weapons), it is difficult to imagine how the possibility of taking action, including the use of force if necessary, could be entirely excluded from the outset. For this reason, Australia has advocated pre-emptive action in such cases, as the report itself notes (p. 10 and footnote 18). But when is such a threat sufficiently 'imminent' to justify armed intervention? Or, in terms of the Caroline doctrine, when is the threat sufficiently instant and overwhelming, leaving no choice of means and no moment for deliberation? Only when the button is about to be pressed? Looking to an actual event in recent times: when would the threat of attack on the United States on 11 September 2001 have been sufficiently instant and overwhelming to justify intervention? When the planes were about to hit the buildings? When the hijackers boarded the planes? When they were in the desert being trained for their deadly mission? Or even when they forged their plans? Or possibly at the moment when Al-Qaida declared war on the US and the West? Difficult questions, which demonstrate the vital importance of reliable intelligence.

We should note that in neutralising a specific threat it is not always necessary to use large-scale force against a country. In some cases limited actions, carried out perhaps by special forces and targeting certain locations or groups, will be sufficient. Such measures resemble police action rather than military action as part of warfare.

New threats and the Charter

The AIV/CAVV wonder whether the 'new threats' are all actually particularly new (pp. 7 and 8). Since they maintain that this is not always the case, the report concludes that the system of collective security set out in the UN Charter is in itself sufficiently flexible to take account of new, genuine security requirements, as long as the potential offered by the Charter is exploited to the full (p. 24). According to the AIV/CAVV, the 'new threats' do not therefore constitute sufficient reason to justify extending the Charter, particularly the interpretation of article 51 (the right of self-defence in response to an armed attack).

The government acknowledges the importance of using all the means available under the Charter to full effect in order to safeguard peace and security. And it should be noted that the Security Council has explicitly labelled new threats such as terrorism and weapons of mass destruction a potential threat to peace and security, as the report rightly observes (p. 24). The UN system has thus shown itself to be flexible and has responded to the new threats.

At the same time, however, it must be borne in mind that the UN system is now almost sixty years old. Immediately after the Second World War, the aim was to eliminate war and violence as standard instruments of foreign policy. Although Article 51 does not restrict the right of self-defence to cases involving an armed attack by a state, the UN system is in principle based on the relations between states. The Charter was not drafted to deal with the 'modern' threats, such as the kind of terrorism we see today, which includes suicide attacks by non-state actors who seek to create as many civilian victims as possible by relatively simple means. Present-day terrorism, potentially combined with weapons of mass destruction, and aided by advances in information technology and mobile communications technology, constitutes a threat that did not exist and could not have been foreseen when the Charter was drawn up. The government therefore believes that new (or perhaps it is better to say 'modern') threats certainly do exist.

In the view of the government, this observation should also have implications for the question of when a threat is imminent. It therefore endorses the statement that 'we must adapt the concept of imminent threat to the capabilities and objectives of today's adversaries' (US National Security Strategy, p. 15). Time may tell whether the Caroline criteria allow sufficient scope for this.

United States security strategy

The government notes that the report does not state that the US security strategy is inconsistent with international law, merely that 'in so far as it goes beyond the Caroline criteria, [it] is not consistent with international law' (p. 22). Apart from the fact that the Caroline doctrine has not yet proved itself in practice, the government does not share the AIV/CAVV's view that the US text sets out no criteria whatsoever that might be used as a means of restricting anticipatory self-defence, apart from a statement to the effect that it may not be used as a pretext for aggression (p. 21). First and foremost, the strategy sets out the firm condition that pre-emptive action may be taken only in response to an 'imminent threat', as the Caroline doctrine does and, according to the report, should. The government would also note that the US security strategy is not a document of international law, but a policy document. Although it does not specifically mention typical doctrines of international law such as the Caroline doctrine, the strategy does contain a number of criteria that have the same practical aim: to subject the unilateral use of force in self-defence to certain conditions (a clear reason, proportionality and a sound justification), as described in the above-mentioned letter of 15 November 2002.

Use of force in emergencies

Besides the legitimate right of self-defence in the case of an impending attack consistent with the Caroline criteria (which does not depend on the approval of the Security Council), the report also considers the possibility that the Security Council might fail to act, even though it might have been expected to do so (section III.5), for example when one of the permanent members exercises its right of veto. 'In the world as it is one cannot close one's eyes to the possibility,' the report rightly points out (p. 33). In the event of military action in such an emergency, the AIV/CAVV believes that the broadest possible consensus in the Security Council, and perhaps also in the General Assembly, must be insisted upon. The government acknowledges the need for the broadest possible support for military action in emergencies other than for the purpose of self-defence.

Assessment framework

The AIV/CAVV believe that there is no point recommending that criteria for pre-emptive action be developed. To anticipate broader-ranging forms of self-defence than those permitted under the Charter would be undesirable, they believe, despite the observation that in emergencies (in cases where the Security Council, even though it might have been expected to act, fails to do so) there will be a need for military action (p. 33).

The government supports the thinking behind this. The basic principle must always be that unilateral use of force should be avoided as much as possible. Drafting a framework within which it would be permitted would therefore be inappropriate.


The government endorses the AIV/CAVV's main conclusion that the right of self-defence may be invoked in the event of 'new' threats, such as terrorism and weapons of mass destruction. It also agrees that the threat must be imminent. It notes that the US security strategy also takes imminent threat as its basis. Whether the Caroline criteria are adequate today for deciding whether a threat is sufficiently imminent to justify exercising the right of self-defence, only experience will tell. While these criteria are a useful tool, one cannot exclude the possibility that they will have to be refined at some point.

Bernard Bot
Minister of Foreign Affairs

Press releases

The press release related to this report has not been translated.