Terrorism is a phenomenon that has been known to mankind for more than two millennia, but over this long period of time, no-one has succeeded in defining terrorism in a manner that is universally acceptable and encompasses all essential elements. 1 Therefore, the frequently utilised word 'terrorism' does not refer to a well-defined and clearly identified set of factual events or to a widely accepted legal doctrine.
The lack of a generic definition cannot invalidate the fact that for several decades, terrorism has been a serious security problem demanding both domestic and international countermeasures. The latter are especially important, as the leading terrorist factions operate internationally in order to gain wider exposure and, as a result, more success, but also to find supporters - namely, states that sympathise with their political objectives. The relevant international countermeasures are naturally associated with the Security Council, to whom the states have conferred primary responsibility for the maintenance of international peace and security. 2 The Security Council, a constantly attentive executive organ, has considerable means, of a broad range, at its disposal for that purpose, starting with diplomatic or economic sanctions and ending with military measures. 3 But before the Security Council can utilise these means, it must first determine whether terrorism falls within its competence. For example, does terrorism constitute a threat to peace that justifies its response?
The present article examines this matter from three perspectives. Firstly, why is the determination of the existence and nature of this situation important? Secondly, what is the nature of a threat to peace in general? Thirdly, can terrorism, generally or specifically, constitute a threat to peace? These questions are discussed in the light of the collective security system envisaged in the United Nations Charter and administered by the Security Council.
The Security Council is a guardian of international peace and security. Although it is composed of only 15 member states 4 , the Security Council acts on behalf of all UN member states when carrying out its duties in connection with maintenance of international peace and security. 5 Despite being a political organ whose decisions are, and also have every right to be, linked to political motivations not necessarily congruent with legal considerations, the Security Council's activity has legal consequences. It is the one organ of the United Nations that can impose legally binding obligations and non-military or military sanctions on the member states. 6 Such means are called (collective) enforcement measures if adopted under the charter's Chapter VII in order to maintain or restore international peace and security.
The Security Council cannot avail itself of enforcement measures at any given moment; it is supposed to follow certain procedure to establish that the conditions for the use of such measures are satisfied. The primary condition is the existence of a threat to peace, a breach of the peace, or an act of aggression. 7 Through the construction of the sentence in Chapter VII 8 , the determination that a relevant situation has arisen is clearly singled out as a condition for the exercise of powers described in said chapter. 9 So, once a positive determination is made, the door is automatically opened to enforcement measures of a non-military or military nature. 10 Nevertheless, this is a procedural rather than substantive limitation, basically demanding that the Security Council as a collective organ reach consensus before imposing enforcement measures. Yet such a limitation may equally help to ensure consistency in the Security Council's practice if the determination is not made on the basis of political expediency but after a genuine assessment of the situation and comparison of the latter with other, similar situations.
The practice demonstrates that the Security Council has not always determined that a threat to peace, a breach of the peace, or an act of aggression existed before it imposed sanctions. The situation in Kosovo had deteriorated to such a point by March 1998 that the Security Council decided to impose a mandatory arms embargo on the Federal Republic of Yugoslavia, including Kosovo, without first determining the situation. 11 For the first time, the Security Council dispensed with declaring that the application of its powers under Chapter VII was based on a determination that there was a threat to peace. 12 Later the United Kingdom insisted that such determination was implied 13 , but the Russian Federation declared, while voting in favour, that the situation under consideration did not constitute a threat to peace. 14 If a majority had shared the latter position, the resolution in question would have been an ultra vires act.
Two more aspects should be taken into account. Firstly, there is no need to expressly refer to Article 39 when making the determination. Indeed, in a significant number of resolutions, the Security Council has established the threat to peace without a proper reference and therefore leaving the legal basis in doubt. 15 Secondly, a determination is not necessary in cases of resolutions following on from previous resolutions that did contain a determination. The latter are cited in the preambles to the former; therefore, the necessary link and legal basis are established. 16 In terms of time, the validity of a determination does not expire 17 ; that is, it remains valid until the Security Council decides otherwise, even if there is a change in the facts on the ground. While the keeping in place of enforcement measures inevitably implies that the threat continues to exist 18 , one cannot generally infer from their suspension or termination that there has been a reduction in threat 19 , because such a step may well be influenced by considerations of a humanitarian nature or by the wish to further encourage a peace process. 20 In other cases, the removal of an item from the Security Council's agenda or the termination of enforcement measures as their objective has been achieved leaves no doubt that, at least temporarily, the threat to peace has ceased to exist. 21
The discretionary power of the Security Council is very broad under Article 39, in terms of decision of both when to act and how to act. At the San Francisco Conference when the United Nations Charter was adopted, various proposals were made that the regulations should be more detailed with regard to the conditions for the applicability of Chapter VII, but, in the end, the present wording was preferred. 22 It was expressly stated that the lack of more specific criteria was necessary if the Security Council were to be allowed to decide how to act on a case by case basis. 23 Therefore, the International Criminal Tribunal for the Former Yugoslavia has aptly stated that "it is clear [...] that the Security Council plays a pivotal role and exercises a very wide discretion". 24 However, there are some who adhere to a view that discretion is not unlimited here. 25 The legal source of potential limitations remains unclear.
A determination is essentially a judgment based on factual findings and the weighing of political considerations that cannot be measured by legal criteria. The latter usually prevail. As a result, the decisions made in the interest of international peace and security are almost exclusively taken in accordance with (national-level) political considerations. 26 The political nature of Article 39 is further emphasised by the fact that the permanent members 27 of the Security Council have a power of veto. However, as a non-judicial organ, the Security Council is not required to give reasons for its decisions. 28 Nonetheless, once it has made a determination, this is conclusive and all member states must accept the Security Council's verdict, even if they do not share its opinion. 29
The Security Council is not obliged to make a determination and subsequently take any enforcement measures. 30 Both the drafting history of the United Nations Charter and the practice of the Security Council indicate that the council does not have to respond to all situations that would seem to call for exercise of its competencies but, rather, operates selectively and with discretion. 31
'Threat to peace' is the most flexible and dynamic of the three terms in Article 39, and it is here that the Security Council enjoys the widest discretion. It is equally true that within this discretion lies the possibility of subjective political judgment. Hans Kelsen has expressed concern that the "threat to peace [...] allow[s] a highly subjective interpretation" 32 , but at the same time claimed that "it is completely within the discretion of the Security Council as to what constitutes a threat to the peace". 33 Michael Akehurst worded this position perhaps even more bluntly by stating that "a threat to the peace is whatever the Security Council says is a threat to the peace". 34 This is the accepted reality nowadays. Obviously, here one should distinguish this discretion from the necessity of sufficient explanation to the states of the characteristics of a specific threat to peace. While this may not be necessary in cases of more traditional threats (preparing an armed attack against a state), it may well be vital if the Security Council is referring to a continuous state of affairs (inability to demonstrate the denunciation of terrorism)...