For an Effective and Legitimate Jurisdictional Regime on the Crime of Aggression at Last: States Parties to the Statute of the International Court to Convene on Monday for a Special Session in New York

As of Monday, a window of historic opportunity will be open for States Parties to the Rome Statute of the International Criminal Court (ICC Statute) for three days to provide the Court with a more effective and more legitimate legal framework for the exercise of jurisdiction over the crime of aggression. The following blogpost sets out why the short and concise amendment proposal, which States Parties will find ready for adoption when they convene for a Special Session of their Assembly, is sound as a matter of law and eminently sensible as a matter of legal policy and that there is no good argument in support of the last minute-attempt by some States Parties to defer the badly needed reform to an uncertain moment in the future.         

1. The Harmonization Amendments and its Proposed Entry Into Force

On 7 April 2025, the Secretary-General of the United Nations, acting in his capacity as depositary of the ICC Statute, circulated amendments to Article 15bis of the Statute proposed by Costa Rica, Germany, Sierra Leone, Slovenia, and Vanuatu which are based on preparatory work of a larger cross-regional group of States.

The proposed amendments aim at harmonizing the International Criminal Court’s (ICC/the Court) exercise of jurisdiction over the crime of aggression with the Statute’s default jurisdictional regime that applies to genocide, crimes against humanity and war crimes. Most significantly, they would remove the exceptions in Article 15bis (4) and (5) that seriously curtail the prosecution of the crime of aggression following a State party referral or a proprio motu investigation, which States introduced as part of the consensus adoption of the Kampala amendments on the crime of aggression at the First Review Conference of the Rome Statute in 2010.

15 years and several acts of aggression later, it has become plain for all to see that the unique restrictions on the ICC’s jurisdiction over the crime of aggression constitute a double standard that is detrimental to the international justice project and that undermines the legitimacy of the ICC (see e.g. Kress, Grzebyk, Nsereko, GIPA). The proposed harmonization amendments address these shortcomings by deleting the current text of Article 15bis (4) and (5) and by introducing language that mirrors Article 12 (2) and (3). As a consequence, the Court’s default jurisdictional regime would apply to the crime of aggression (for details see MacDougall, Reisinger Coracini, Trahan). It is important to note that the proposed amendments target precisely those provisions that created the gap in the Court’s jurisdictional reach. They do not question the valuable procedural guarantees in Article 15bis (6)-(9). 

The proposed amendments were submitted on the basis of Article 121 (1), which allows any State Party to propose amendments to the ICC Statute after the expiry of seven years from its entry into force. More importantly, the proposal has been submitted in the context of the mandatory review of the aggression amendments seven years after the beginning of the Court’s exercise of jurisdiction, as mandated by States Parties in Kampala (RC/Res.6, para. 4). While a ‘review’ does not necessarily require the adoption of harmonization amendments, such amendments fall squarely within the Assembly’s mandate. The proposed amendments were circulated three months before the beginning of the review of the Kampala amendments at the Special Session of the Assembly of States Parties to be held from 7-9 July 2025 in New York (ICC-ASP/23/Res.1, para. 16(b)) and therefore fulfil the procedural precondition set out in Article 121 (2) of the ICC Statute, allowing States Parties to decide whether to take up the proposal at the Special Session.

The proposed amendments deal with the substantive aspects of harmonizing the Court’s exercise of jurisdiction. They neither address the relationship of the harmonization amendments with the Kampala amendments, nor the entry into force mechanism. These issues are addressed in a ‘Draft Resolution on the Crime of Aggression, Article 15bis Rome Statute’, submitted by a group of states on 5 June 2025. The latter stipulates that the amendments, once adopted by consensus or by a majority of 2/3rds of States Parties (Article 121 (3) ICC Statute), shall enter into force for those States Parties that have accepted them one year after the deposit of their instruments of ratification or acceptance (draft Resolution OP 1). It is thus based on the entry into force mechanism of Article 121 (5) first sentence.

This post sets out to explain why this approach is sound as a matter of law and compelling as a matter of policy (see infra 2 to 4). Following this, the text explains how the activation of Article 12 (3), as envisaged by the harmonization proposal would operate (infra 5) and how the harmonization amendment, if adopted, would interrelate with the Kampala amendments (infra 6). In conclusion, we appeal to States Parties to the ICC Statute not to let pass before them the historic opportunity to make the Court’s jurisdictional regime more effective and more legitimate by adopting the harmonization proposal next week in New York.    

2. The ICC Statute’s Legal Framework for the Entry into Force of Amendments and the Peculiar Challenge of Applying this Framework in the Case of the Crime of Aggression

Leaving aside Article 122, which is applicable to several provisions of an institutional nature, the ICC Statute contains two entry into force mechanisms for amendments: Article 121 (5) first sentence provides for a subjective entry into force mechanism. Amendments to Articles 5, 6, 7, and 8 enter into force only for those States Parties that accept them, one year after the deposit of their instrument of acceptance. The provision does not establish any quantitative threshold for the entry into force of an amendment. It is accompanied by a second sentence which formulates conditions for the exercise of the Court’s jurisdiction over ‘amended crimes’.

With a view to all other articles, Article 121 (4) foresees an objective entry into force mechanism. Once 7/8ths of States Parties have accepted the amendments, they enter into force for all States Parties. At the same time, the Statute offers States Parties that have not accepted the amendments the possibility to withdraw from the Statute with immediate effect (Article 121 (6)). A majority of 7/8ths would currently equate to 109 states. But it should be kept in mind that the exact number of required States is a moving target as it depends on the number of States Parties at the relevant time.

The application of this legal framework to the crime of aggression presents a peculiar challenge: The crime of aggression found its way into the ICC Statute only in the course of the final hours of the Rome diplomatic conference, and States Parties decided to accord to this crime a distinct place. While Article 5(1)(d) of the ICC Statute as adopted in 1998 included the crime into the ICC’s jurisdiction from the outset, Article 5(2) stipulated that the Court’s exercise of jurisdiction over the crime was suspended pending both its definition and the setting of the conditions for the exercise of jurisdiction over it. This political compromise has led to an inextricable connection between the formulation of the definition of the crime and the conditions for the exercise of jurisdiction over it. The ICC’s amendment provisions were thus negotiated and finalised without having in mind the distinct compromise regarding the crime of aggression including, in particular, the inextricable connection between substance and procedure. This explains why none of the options for the entry into force in Article 121 of the ICC Statute provide a neat fit for an amendment fulfilling the mandate given to States Parties in Article 5 (2) to define the crime of aggression and to set out the conditions for the Court’s exercise of jurisdiction over that crime.

More specifically, Article 5 (2) stipulates that such a provision shall be adopted in accordance with Article 121 and thus directly links to paragraph 3 of Article 121, which requires consensus or the affirmative vote of 2/3rds of States Parties for the adoption of an amendment. Article 5 (2) does not say anything further as regards the entry into force. An interpretation of Article 5 (2) in conjunction with Article 121 also remained inconclusive: On the one hand, the provision on aggression did not require an amendment to Articles 5, 6, 7, or 8, which pointed towards entry into force in accordance with Article 121 (4). On the other hand, the definition of the crime of aggression, which was an essential part of the amendment provision, concerned the Court’s subject matter jurisdiction and thus bore far more resemblance to the scope of application of the entry into force mechanism in the first sentence of Article 121 (5) than with that in Article 121 (4).

In this situation, States considered the possibility of applying the first sentence of Article 121 (5) to the definition of the crime of aggression and Article 121 (4) to the procedural part of the Kampala amendments. This idea, however, was quickly abandoned for its obvious impracticability: it would have meant that even if parts of the aggression amendments had entered into force for accepting States Parties under the first sentence of Article 121 (5), the relevant procedural amendments would have needed to await acceptance by 7/8ths of the States Parties pursuant to Article 121(4). To avoid such an odd result, States Parties quickly agreed that all amendments relating to the crime of aggression, which form the ‘provision on the crime of aggression’ as mandated in Article 5 (2), should enter into force under the same procedure (ICC-ASP/6/20/Add.1, paras. 6 et seq.; ICC-ASP/7/20/Add.1, paras. 6 et seq.).

All this meant that States Parties were required to make a choice, and the choice they made in Kampala was to proceed in line with the first sentence of Article 121 (5).                        

3. A Legally Sound and Eminently Sensible Proposal: Staying with the First Sentence of Article 121 (5)

The draft Resolution’s proposal to proceed in line with the first sentence of Article 121 (5) follows precisely this Kampala consensus. For the reasons that follow, this proposal is as legally sound as it is the most sensible way forward.  

The proposed harmonization of the ICC’s jurisdiction raises similar amendment issues as States Parties confronted in Kampala, as the substantive and procedural elements of the aggression amendments remain inextricably intertwined.

This is particularly true for non-Kampala States: it is inconceivable they could accept the harmonization amendments without simultaneously accepting the Kampala amendments. Otherwise, a State would be bound only by a fragment of the aggression amendments, that is by the modification of a provision that it continues not to be bound by. Most importantly, non-acceptance of the definition of the crime of aggression in Article 8bis would preclude the ICC from exercising its jurisdiction over a crime of aggression committed against that State (by a non-Kampala State Party or a non-State Party) due to a failure to establish a jurisdictional link under Article 12 (2) as reflected in the proposed amendment of Article 15bis (4).

There is thus no compelling legal reason for States Parties now to change direction with respect to their choice of the entry into force mechanism. Very much to the contrary: The consensus decision of Kampala to apply the entry into force mechanism in the first sentence of Article 121 (5) to the Kampala amendments in their entirety is best understood as an instance of subsequent practice by States Parties to the ICC Statute within the meaning of Article 31 (3) (b) of the Vienna Convention on the Law of Treaties (VCLT) embodying an agreement as to the entry into force of amendments relating to the provision on aggression.

Furthermore, it is a well-established legal principle that an initial act and any eventual act of revocation or modification must be passed upon the same legal authority. The actus contrarius principle thus also serves as a justification to apply the same procedure that was previously used to introduce a provision to amend the provision in question. In other words, the harmonization amendments should enter into force under the same mechanism as the Kampala amendments.

Proceeding in line with the first sentence of Article 121 (5) is also eminently sensible from a policy point of view: The objective entry into force mechanism in Article 121 (4) requires a very high threshold to be passed. The harmonization amendments would only enter into force once 7/8ths of States Parties have ratified them. The advantage of this procedure would be the uniform application of the harmonized jurisdictional regime for all States Parties. But the very serious disadvantage lies in the lengthy period of time that would be required to reach the 7/8ths threshold. States Parties that wish to avail themselves of the legal protection against crimes of aggression could not achieve this result on their own. In the worst, and by no means unrealistic scenario, the harmonization amendments might never enter into force and hence would remain a purely symbolic act.

Proceeding in line with the first sentence of Article 121 (5) means avoiding this very serious disadvantage: it would allow for a gradual expansion of the Court’s jurisdictional reach. By ratifying the harmonization amendments, States could avail themselves of the legal protection of the Court’s jurisdiction against a possible crime of aggression in the future.

Some have spoken of a risk of ‘fragmentation’ in this context. The very real and detrimental fragmentation, however, consists of the fragmentation that currently exists within the ICC Statute, which leaves the Court no choice, but to apply the crimes under its jurisdiction selectively with a marginal place being accorded to the crime of aggression.  

4. The Need to Distinguish Between Entry into Force and Conditions for the Exercise of Jurisdiction – and Hence Between the First and the Second Sentence of Article 121(5)

It is sometimes said that proceeding in line with the first sentence of Article 121 (5) would entail the need to also apply the second sentence of Article 121 (5). This argument, however, ignores the fact that these two sentences are sharply distinct as regards their subject matter: while the first sentence provides for an entry into force mechanism, the second sentence deals with the conditions for the exercise of the Court’s jurisdiction. At the Kampala Review Conference, States Parties decided by consensus that the Kampala amendments should enter into force in accordance with the first sentence of Article 121 (5). At the same time, the Kampala amendments reflect the understanding that the mandate of Article 5 (2) allowed States Parties not to apply the second sentence of Article 121 (5) to the crime of aggression, but to set the conditions for the crime of aggression independently of the latter provision.

The decision made by States Parties in Kampala was legally sound not only because of the explicit wording of Article 5 (2), but also in view of the fact that the crime of aggression was not a ‘new’ crime but one that was under the Court’s jurisdiction from the outset, so that the motivation that underlies the stringent hurdles for the exercise of jurisdiction formulated in the second sentence of Article 121 (5) does not apply in the case of the crime of aggression. What was true in 2010 in Kampala remains valid for the 2025 review of the Kampala amendments. 

A proper understanding of the sharp difference between the subject matter of the two sentences of Article 121 (5) also clears the way for a proper understanding of how these sentences do and do not relate to international treaty law. The first sentence is a direct reflection of a basic rule of international treaty law, more specifically the res inter alios acta rule, according to which a treaty, save for very limited exceptions, creates obligations and rights only for its parties.

In accordance with this basic principle, the first sentence of Article 121 (5) determines ratification or acceptance as the appropriate ‘means of expressing consent to be bound’ (Article 11 of the VCLT) by an amendment to Articles 5, 6, 7, and 8 of the ICC Statute and ensures that ‘the amending agreement does not bind a State party that does not become a party to the amending agreement’ (Article 40 (4) of the VCLT). The second sentence of Article 121 (5) is concerned with something completely different: it stipulates the conditions under which the ICC may exercise its jurisdiction over crimes committed on a certain territory or by certain nationals. The provision thus does not create obligations for States and, in particular, it does not create obligations for States that do not accept the amendment in compliance with Article 34 of the VCLT. Instead, it is addressed at the ICC and directly affects individuals who thereby become exposed to the exercise of the Court’s jurisdiction. Any attempt to read the second sentence as a necessary corollary of the treaty law principle of res inter alios acta rule is therefore misconceived.

5. Ad Hoc Acceptance of the Court’s Jurisdiction Over the Crime of Aggression

The proposed harmonization amendments aim at removing the jurisdictional restrictions introduced into the ICC Statute by the Kampala amendments. These restrictions include the inapplicability of Article 12 (3) which, inter alia, enables the Court to exercise its jurisdiction over conduct committed on the territory of or by nationals of a non-State Party where that State has consented to such an exercise of jurisdiction by virtue of a declaration submitted ad hoc with respect to the situation concerned. The amendment proposal for a new Article 15bis (5) thus explicitly provides that Article 12 (3) would also apply to crimes of aggression and hence to all four crimes within the Court’s jurisdiction equally.

The proposed amendment of Article 15bis (5) would also allow States Parties that have not accepted the Kampala amendments to accept the Court’s jurisdiction over the crime of aggression on an ad hoc basis in accordance with Article 12 (3). This does not constitute an amendment of Article 12 (3). It just makes Article 12 (3) applicable in conformity with its text and spirit. For non-Kampala States Parties possess the status of a non-State Party as far as the Kampala amendments are concerned. To proceed otherwise would result in an absurdity, as it would withhold to a State Party to the ICC Statute the power flowing from Article 12 (3) as regards the crime of aggression while giving the same power to a State which is not party to the Statute.

If the harmonization proposal enters into force in line with the first sentence of Article 121 (5), the new Article 15bis (5) will be activated one year after the ratification of the harmonization amendments by one State Party. The same logic led drafters of the Kampala amendments to the conclusion that one ratification would suffice to activate Article 15ter and allow the Court to exercise its jurisdiction over the crime of aggression in the case of a UN Security Council referral to the Court of the relevant situation (ICC-ASP/7/20/Add.1, paras.28 et seq and Appendix II).

The Kampala compromise introduced temporal conditions for the exercise of jurisdiction over the crime of aggression for all trigger mechanisms. Common paragraphs 1 and 2 of Articles 15bis and 15ter eventually both included a minimum threshold of 30 ratifications and a requirement that the Assembly of States Parties make a further decision to activate the ICC’s jurisdiction over the crime of aggression (see ICC-ASP/16/Res.5). It is important, however, to stress that these temporal conditions were not required by the ICC Statute and did not constitute an amendment to Article 121 (5), but that they constituted further conditions for the exercise of the Court’s jurisdiction that States Parties considered themselves authorized to set in fulfilling their mandate under Article 5 (2) of the 1998 ICC Statute, and were the outcome of a political compromise.

To date, ad hoc acceptances of the Court’s jurisdiction have primarily been used as a tool to extend the Court’s temporal jurisdiction back in time (for an incomplete record, see here). This conforms to the prevailing interpretation of Article 12 (3) in conjunction with Article 11 (2). Under this interpretation, a State that becomes a party after the entry into force of the Statute on 1 July 2002 can enable the Court to exercise temporal jurisdiction over crimes committed before the entry into force of the Statute for that State in line with the retrospective effect specified by the State concerned in a declaration submitted under Article 12 (3).

In the context of the harmonization proposal, the question has arisen as whether the ad hoc acceptance of the Court’s jurisdiction over the crime of aggression as envisaged in the proposed Article 15bis (5) would include the possibility of expanding the Court’s temporal jurisdiction to a time before the entry into force of the harmonization amendments. Such a temporal extension is currently neither explicitly provided by the proposed harmonization amendments nor by the draft Resolution. A strong argument has been made that the prohibition of retroactivity contained in the Statute precludes the possibility of a State providing the Court with the power to apply the new paragraphs 4 and 5 of Article 15bis retroactively to conduct that has taken place before their entry into force (MacDougall). But to make a purely prospective application of the harmonization amendments legally watertight, States could add a paragraph in the draft resolution to this end.

6. The Interrelation Between the Harmonization Amendments and the Unamended Kampala Amendments  

Kampala States that wish to be bound by the harmonization amendments simply need to ratify or otherwise accept them.

This would not, however, be sufficient for States Parties that have not yet accepted the Kampala amendments or for States that are not yet parties to the Statute. This is so because the harmonization amendments replace but one element of the Kampala amendments and would not be operable without the remainder of them. For example, neither non-Kampala States Parties nor States not party to the Statute would become bound, by the definition of the crime of aggression in Article 8bis contained in the Kampala amendments by virtue of an acceptance to be bound by the harmonization amendments. In view of this inextricable linkage between the harmonization amendments and the Kampala amendments, the draft Resolution suggests that the harmonization amendments and the Kampala amendments form an inseparable package.

In view of this, the draft Resolution proposes in its OP 3 that non-Kampala States Parties cannot accept either the harmonization amendments or the Kampala amendments without the other. There is no legal impediment for States Parties to set such a condition in the enabling Resolution. To accept the harmonization amendments and the Kampala amendments as a package is also in the interest of non-Kampala States Parties. For only by proceeding in that way, will those States secure full legal protection in case of a crime of aggression committed against them by a State that has not accepted the aggression amendments.  

The situation is different with respect to States not party to the ICC Statute. Four different possibilities require consideration in case of the adoption of the harmonization amendments. The following two of them do not require any further explanation: Clearly, future States Parties could adhere to the Statute, as amended by the Kampala amendments and the harmonization amendments. Consistent with existing practice, such States would also remain in a position to adhere to the Statute without accepting any aggression amendment.

It has, however, been questioned whether States Parties can prevent future States Parties from accepting only the Kampala amendments. Article 40 (5) (a) of the VCLT provides that “[a]ny State which becomes a party to the treaty after the entry into force of the amending agreement shall, failing an expression of a different intention by that State: be considered as a party to the treaty as amended”. In other words, the provision favours the assumption that a State would become a party to the amended treaty, but a State may declare its intention to become a party to the treaty in its unamended form. This provision is, however, a default one; a treaty may provide otherwise (Article 40 (1) VCLT) and require a State that wishes to adhere to a treaty to become bound by the treaty only in its amended form. The ICC Statute is silent on the matter, and previous practice regarding amendments entering into force under Article 121 (5) leaves aspiring States Parties the option to accept the ICC Statute in its unamended or one of its amended versions. This practice, as well as the underlying amendment regime of Article 121 (5) itself, have led to an unfortunate fragmentation of the Court’s jurisdictional framework.

For this reason, it would be desirable that States not party to the Statute accept the Kampala amendments and the harmonization amendments as a package in the same manner as OP 3 mandates in case of non-Kampala States Parties. It is difficult to see why States Parties, being the masters of their treaty, should be legally prevented from posing a condition to that effect in their enabling resolution. But in light of their previous practice, States Parties seem reluctant to proceed in that way. The draft resolution, therefore, contains no more than an encouragement to do so. This mere encouragement should not give rise to worries, as it is hard to see why a State not party should be interested in adhering to the Statute with the Kampala amendments, but without the harmonization amendments, because only together the State concerned would secure full legal protection against a crime of aggression committed against it.     

The fourth and last possibility for a State not party to the Statute would be to adhere to the Statute with the harmonization amendments, but without the Kampala amendments. Obviously, such an approach would not be sensible because the adhering State would not hereby become bound by the definition of the crime of aggression in Article 8bis and would therefore not provide the Court with a jurisdictional link under Article 12(2). Again, the State concerned would not enjoy full legal protection against a crime of aggression committed against it. There would be no legal impediment for States Parties to include in the enabling Resolution a provision to the effect that States not party to the Statute can adhere to the Statute with the harmonization amendments only together with the Kampala amendments. At the Special Session, States Parties might wish to consider the inclusion of such a provision into the draft resolution.    

7. No Time to Delay – An Appeal to States Parties

The foregoing explanations have shown the following: The proposals for a harmonization amendment and its entry into force are sound as a matter of law and eminently sensible as a matter of legal policy. While some finetuning of certain elements of the proposed enabling Resolution certainly remains possible, the proposed reform for a more robust and more legitimate jurisdictional regime in the ICC Statute for the crime of aggression is ready for adoption.

Nevertheless, on 27 June 2025, Canada, France, Japan, New Zealand and the United Kingdom have submitted the proposal to defer such a decision. The central argument is that the Kampala amendments have been accepted ‘only’ by 48 States Parties thus far and that it would thus be preferable first to wait and see whether more States Parties are willing to adhere to the Kampala amendments. This argument, however, is flawed: it ignores the fact that many States Parties have withheld their acceptance of the Kampala amendments precisely because they consider them ineffective and unprincipled. As South Africa’s Kampala delegate André Stemmet astutely predicted: ‘The major weakness is, of course, that Non-State Parties (…) will be able to commit aggression with a sense of impunity, and this reflection of realpolitik may result in a very slow process of ratification and acceptance.’

One other argument that was made in support of ‘postponement’ points to the difficult situation in which the Court presently finds itself and to therefore abstain from adopting the reform proposal now. Also this argument fails to convince: While the description of the present situation of the Court is certainly true, apart from its being an understatement, the conclusion to draw from the serious threats the Court is currently facing should not be to miss a historic opportunity to strengthen the Court and to eliminate a double standard that is haunting it. The right way forward for States Parties in this challenging situation is precisely the opposite: to stay calm and resolve to make the Court’s legal framework more effective and legitimate with regard to the crime of aggression – not in an uncertain future, but now.