The words ‘historic achievement’ suffer from inflation. In the field of international law, these words should be reserved for events that can truly qualify as major steps in the development of this field of law. The adoption of the Rome Statute of the International Criminal Court (ICC) in 1998 was such an event. The adoption by the ICC Review Conference of the package proposal on the crime of aggression,Footnote ¹ on 11 June 2010 in Kampala, was also such an event. The adoption of this package concluded decades of preparatory work and is a decisive step in the completion of the Rome Statute. Fundamental issues were involved, creating hurdles before the finishing line could be reached. Before the Review Conference pessimism prevailed as to the likelihood that agreement could be reached. To many, the hurdles on the way seemed almost insurmountable.Footnote ²

The result at Kampala is even more remarkable in that the most difficult issue on the table was still unresolved at the start of the conference. While preparatory work had been successful in formulating a definition of the crime of aggression – in itself a major achievement – it failed to provide even the beginning of a solution on the question of the conditions for the exercise of jurisdiction over the crime of aggression by the ICC. Therefore the hardest nut still had to be cracked in Kampala.

Those present in the conference room will not forget the dramatic final hours of decision-making. Clocks had to be stopped at 24.00 and were removed. At 00.20 the president presented his ‘best attempt to achieve a compromise’ and asked whether it was the wish of the Review Conference to adopt the package by consensus. At that moment, it was uncertain for almost all participants whether or not the silence would be broken, blocking a consensus decision. Most eyes were fixed on the delegations of France and the United Kingdom, which had firmly and consistently indicated that the compromise package was undermining the position of the UN Security Council. Only France and the United Kingdom had to reconcile their loyalty to the ICC with their loyalty to the Security Council and its five permanent members (P-5). At the end of the day their wish for a consensus agreement on aggression prevailed and they could live with the result. However, unexpectedly, the delegate from Japan raised his hand. A shock was collectively felt. When the Japanese delegate stated that he had asked for the floor ‘with a heavy heart’, almost everyone in the room was convinced that the attempt to reach consensus had failed. The depth of this shock was only equalled, and even surpassed, by the depth of the collective release when, a few sentences later, Japan explicitly stated that it did not want to break the consensus. Long applause and cheering followed, a bagpipe played, other scenes occurred that are rather unusual in diplomatic settings.

In the following, we shall briefly focus on three key issues: consensus as a decision-making technique, the substance of the agreement, and the impact of the decision on the Security Council.

1. The power of consensus

The Review Conference had to adopt amendments by consensus; if no consensus could be reached, decisions could also have been taken by a two-thirds majority of the states parties. These decision-making rules are similar to those of many international organizations. The advantage of decision-making by consensus is that it puts the collective strength of the members behind the decision, offering the best possible guarantee for full implementation. Disadvantages are the slowness of this way of decision-making and the possibility that a single member may block the consensus. The threat of a vote is therefore crucial. The key conditio sine qua non for successful decision-making by consensus is the chair of the meeting. The chair must have the authority, the expertise, and the experience actively to guide the process, to maintain good relations with all participants and have their full confidence, and to intervene whenever necessary.

The Kampala agreement on aggression is a model example of decision-making by consensus, except for one element. It is highly uncertain that the threat of a vote was a real threat. Seventy-four votes in favour would be necessary to adopt amendments. However, only a few more than 74 states parties were represented. Some delegations were due to leave on Friday evening or Friday night (11 June). Behind the scenes calculations were being made during the two weeks of the Review Conference. Proxy voting was being considered. Some states were not entitled to vote, as they were in arrears in the payment of their contributions. In addition, some delegations had to seek new instructions when no decisions could be taken by consensus; it is difficult to see how such new instructions could have been obtained late Friday night.

However, apart from this highly uncertain ‘threat of a vote’, the Kampala agreement was a textbook example of decision-making by consensus. Almost every state party from the outset indicated that it had a strong preference for consensus decision-making or even that it did not want to vote as this would be divisive for the ICC. The logical consequence of aiming for consensus is that there must be flexibility and willingness to compromise, and this was demonstrated by all the parties in Kampala. The role of the president in Kampala was exemplary. From June 2009 until the finale of the negotiations, the crime of aggression negotiations were chaired in an impressively wise and able manner by Prince Zeid Ra'ad Zeid Al-Hussein (Jordanian ambassador to the United States and the first president of the Assembly of States Parties). The president of the Review Conference, the Liechtenstein ambassador to the UN, Christian Wenaweser, had most ably chaired the Special Working Group on the Crime of Aggression (2002–9) and demonstrated strong, determined leadership in Kampala. He was assisted by an excellent team in which Stefan Barriga was the impeccable mastermind, both on substance and on process. There is no alternative history, but it is unlikely that there would have been this agreement on aggression without such strong leadership.

2. Key elements of the crime of aggression agreement

One key element of the crime of aggression compromise is that a final decision still has to be taken, not before 1 January 2017, before the ICC will actually have jurisdiction over the crime of aggression. The states parties therefore still must activate such jurisdiction. Moreover, after this decision has been taken, the ICC may exercise jurisdiction only with respect to crimes of aggression committed at least one year after the ratification or the acceptance by thirty states parties of the amendments. However, while the ICC will therefore not automatically have jurisdiction over these crimes in the future, it is generally expected that it is the wish of the overwhelming majority of the states parties to activate this jurisdiction and to ratify the amendments.

This ‘postponed exercise of jurisdiction’ also addresses the frequently raised concern that the ICC is ‘too young’ to handle the crime of aggression. Whatever the merits of this concern, it is crucial that the way in which the ICC exercises its functions in relation to this special crime is solid, carefully prepared, and preferably generally agreed. In that respect, it may be an advantage that both states parties and the ICC – perhaps somewhat taken by surprise in view of the unexpected adoption of the crime of aggression package – now have ample time to prepare for the entry into force of the amendments. The implementation of this agreement at the national level will need to address difficult questions of jurisdiction and immunity. The ICC has to adapt its structures so as to enable the Pre-Trial Division to fulfil its new function. No doubt all this preparatory work could bring to the fore new questions. However, this will not affect the decisive step that has now been taken.

It is to be expected that an activation decision will be taken not too long after 1 January 2017. While it is therefore true that it will be a number of years before the ICC is eventually in a position to exercise its jurisdiction over the crime of aggression, it is even more true that the criminalization of aggression is a long-term process. Against the background of the long and complex history of the crime of aggression, the period of seven-plus years now required before the ICC has effective jurisdiction over this crime is acceptable and even sensible.

The Kampala compromise left both the draft substantive definition of the crime and the draft elements of the crime as they resulted from the preparatory workFootnote ³ untouched.Footnote ⁴ Remarkably, in Kampala the United States did not insist on reopening the debate on the respective drafts. Instead, the US delegation recognized the missed opportunity to influence the debate within the Special Working Group on the Crime of Aggression. Yet the United States submitted a set of draft understandings pertaining to the draft definition with a view to further clarifying the latter. Understandably, this initiative met with considerable reluctance in the light of the delicacy of the matter and the lateness of the hour. At the same time, however, there was a sense of appreciation of the constructiveness of the new US approach and of the longer-term importance of not simply rejecting what seemed to be an honest US attempt eventually to engage in the debate. As a result, the German delegation was entrusted with the task of facilitating consultations on the US proposals. These talks finally led to the adoption of two understandings that are specifically devoted to the state component of the crimeFootnote ⁵ and which, in different ways, emphasize the fact that it is only participation in serious and unambiguous violations of the international prohibition of the use of force that give rise to individual criminal responsibility for the crime of aggression. The constructive Kampala consultations on these understandings have probably contributed to a positive climate for reaching the final consensus decision on the crime of aggression.

Apart from this, and as was to be expected, the negotiations in Kampala centred on the vexed and intimately intertwined issues of the conditions for the ICC's exercise of jurisdiction and the entry into force of the aggression amendment. A consensus solution only became possible when, on the final day of the conference, the delegations of the United Kingdom and of France had to realize their isolation within the community of states parties to the Rome Statute.

The jurisdictional part of the Kampala package sets up two distinct schemes depending on whether the proceedings are being triggered by the Security Council or, respectively, by a state party or the Prosecutor. The power of the Security Council to trigger aggression proceedings has always been uncontroversial. Remarkably, however, under the Kampala package the Security Council need not make a determination of the existence of an act of aggression. Instead, the Security Council's ‘green light’, as implied in its referral of a respective situation to the ICC, will do.Footnote ⁶ This allows for more flexibility in the Security Council's decision-making, which might prove helpful should the Security Council wish to retain its past conspicuous reluctance to make a determination that an act of aggression has occurred.

How to go about the two other trigger mechanisms, as enshrined in paragraphs (a) and (c) of Article 13 of the ICC Statute, amounted to the ultimate bone of contention. The final solution does not subject aggression proceedings to the conditio sine qua non of a prior Security Council determination of the existence of an act of aggression or to another form of Security Council ‘green light’.Footnote ⁷ The Kampala compromise hereby reflects the strongly felt preference of the overwhelming majority of states parties. At the same time, the jurisdictional scope for ICC action on the crime of aggression in cases of Security Council inaction will remain a very limited one for quite a time to come. This is so, first, because the ICC will be precluded from exercising jurisdiction over the crime of aggression with respect to acts of aggression by and against non-state partiesFootnote ⁸ and, second, because the exercise of jurisdiction in cases of acts of aggression committed by one state party against another will be governed by the consent principle. Interestingly, the technique by which the latter principle will operate does not reflect the formulation of the second sentence of Article 121(5) of the ICC Statute because of the opt-out regime that is to apply with respect to an alleged aggressor state.Footnote ⁹ It is, above all, this part of the compromise that has led Japan, in particular, to raise legal questions. These questions require a detailed answer which exceeds the scope of the present impressions from Kampala. Suffice it to state at this juncture that the negotiators found themselves in a specially challenging situation because the reference to ‘articles 121 and 123’ as contained in Article 5(2) of the ICC Statute, only on a somewhat closer inspection, proved to be fraught with very considerable ambiguity.

One last procedural element of the Kampala package on aggression deserves to be mentioned. Where aggression proceedings are triggered by a state party or by the Prosecutor, the entire Pre-Trial Division has to authorize the commencement of investigations.Footnote ¹⁰ This specific institutional device complements the substantive requirement that the state act of aggression must constitute a manifest violation of the Charter of the United Nations.

3. The Kampala compromise and the Security Council

After the consensus decision had been reached, the five permanent members of the Security Council declared their dissatisfaction with and their legal doubts about the rejection of a Security Council monopoly with respect to the conduct of proceedings for the crime of aggression before the ICC. As had been the case throughout the negotiations, however, these statements were not supported by anything close to an elaborate argument. Contrary to the P-5's cetero censeo, the conformity of the rejection of a Security Council monopoly over the Charter of the United Nations is beyond serious argument, as has been demonstrated on numerous occasions in the course of the recent debate on the subject.Footnote ¹¹ The Security Council retains the full panoply of its powers with respect to cases of aggression under the UN Charter. These include the competence to defer criminal proceedings before the ICC in accordance with Article 16 of the ICC Statute, as is reaffirmed in the Kampala compromise.Footnote ¹² Based on and in accordance with Chapter VII, the Security Council may also give directions directly to its member states with respect to any ongoing ICC proceedings. It is thus only the P-5's legally unwarranted claim to a monopoly right with respect to proceedings for the crime of aggression that has been rejected in Kampala.

It is much to be welcomed that the United Kingdom and France eventually decided not to block the consensus on the basis of their claim to a Security Council monopoly. It would be mistaken, however, to interpret this final move as the acceptance of a weakening of the paramount Security Council's powers in the field of international peace and security. By eventually refraining from overstretching their competences, the United Kingdom and France have made a wise decision which can only be conducive to strengthening the acceptance of their privileged position as permanent members of the Security Council. It is much to be hoped that, over time, all permanent members will come to accept that the decision made in Kampala does not constitute an attack on the Security Council's special role and the permanent members’ special position therein. With respect to the crime of aggression the same applies as for the ICC's entire field of jurisdiction: a world order of peace and justice is best served by co-operation instead of confrontation between the ICC and the Security Council.