The Crime of Aggression: Adding a Definition to the Rome Statute of the ICC

Anja Seibert-Fohr
November 18, 2008


In July, 1998, the Contracting States at the Rome Diplomatic Conference for an International Criminal Court (ICC) could not agree on a definition of the crime of aggression.[1] Thus, while the crime of aggression was included in the Rome Statute as one of the core crimes, it remains non-operational until a provision is adopted defining the crime and setting out the conditions for the exercise of jurisdiction.[2] Though the States Parties were long stalemated on the question, progress has been made lately. The last meeting of the Special Working Group took place in June 2008.[3] Before the States Parties will be in a position to adopt a definition, disagreement over the role of the UN Security Council in referrals to the ICC, and also over the procedure through which both the definition and referral mechanism can be included as an amendment to the Rome Statute, must be resolved.


The international prosecution of crimes against peace began with the Nuremberg and Tokyo Trials of the Major War Criminals sixty years ago.[4] Apart from the post-World War II judgments, there have not been any significant cases of implementation. Efforts over the years to codify the crime proved to be complicated because of highly controversial issues, such as the scope of the right to self-defense, the legality of humanitarian intervention, and the role of the Security Council.[5] Although the Contracting States did not agree to a definition in the Rome Statute, the Assembly of States created a Special Working Group on the Crime of Aggression in 2002.[6] An amendment to the Rome Statute on the crime of aggression is scheduled for the ICC review conference in 2010. In preparation for the review, the Working Group has been holding regular meetings during the sessions of the Assembly of States and inter-session meetings at the Woodrow Wilson School of Princeton University. The group is open to all interested States -- not just States Parties -- so that States such as Russia and China can also take part in the meetings. With its decision not to become a party to the Rome Statute, and the American Service-members' Protection Act of 2002[7] ruling out collaboration with the ICC, the United States government does not participate.

Current State of Negotiations

In the face of skepticism by international legal scholars about the prospect of reconciling different approaches among States Parties, and despite earlier difficulties, the Working Group has made recent progress on drafting an amendment on aggression.[8] This progress is due to the decision to consider the definition of aggression and the exercise of jurisdiction over the crime of aggression separately. In May 2008, the Chairman distributed a draft amendment that included a definition of aggression.[9] There is agreement that the definition should be grounded in the United Nations General Assembly resolution on the definition of aggression.[10] However, it is still controversial whether the resolution should be referred to explicitly in the amendment.

The current draft amendment takes a conservative approach, defining the crime of aggression as a “leadership crime” which only applies to manifest violations of the UN Charter. Among the listed acts of aggression are: (1) the military invasion or attack of another State’s territory; (2) bombardment of such territory; (3) military blockade of foreign ports and coasts; and (4) attacks on land, sea and forces of another State. Situations in which foreign forces, territory or irregular groups are used to carry out such acts are also covered.

The role of the UN Security Council in referral remains unsettled. While France and the United Kingdom favor requiring the Council to take an affirmative decision to trigger ICC jurisdiction over the crime of aggression, a majority of States Parties advocate an arrangement in which action by the Council would not be necessary to trigger an investigation, but would be permitted to prevent an investigation. The difference would become relevant in situations of political disagreement among the permanent members of the Council. With the first approach, political deadlock would prevent any referral and thus any prosecution; with the second, such political deadlock would not prevent the ICC from pursuing charges.

The Amendment Procedure

A less political but nonetheless significant question is how to adopt the definition of aggression into the Rome Statute, a question which was discussed but left unresolved at the June 2008 meeting. According to Article 5 (2) of the Rome Statute, a provision on aggression needs to be adopted in accordance with Article 121. This provision provides for different procedures depending on the content of an amendment: Amendments to Article 5 through 8 – the crimes within the jurisdiction of the court - shall only enter into force for those States Parties which have accepted the amendment and thereby affirmatively opt-in.[11] All other amendments will enter into force for all States Parties provided that a seven-eighths majority has ratified or formally accepted it.[12] If a State does not agree with the changes it may opt-out by withdrawing from the entire Statute.[13]

The approach seeks to provide for unitary reform of the Statute where matters of procedure and structure or minor substantive changes are involved. In order to be operable, such rules must be changed with respect to all proceedings. Once a seven-eighths majority is reached, the procedures are put into effect uniformly. A different procedure was chosen for amendments to Articles 5 to 8 because such changes concern the core crimes on which the Court may exercise its jurisdiction. It is consistent with the territorial and national jurisdiction of the ICC to require the consent by each affected State to any changes to the definition of covered crimes.

The Working Group Discussion

With current discussions of the definition of the crime of aggression progressing at the Working Group, some States Parties now favor uniform revision of the Rome Statute without an opt-out mechanism. They seek universal application of the crime. The definition of aggression, in their opinion, is not an amendment to the core crimes, but the completion of a process agreed upon and started in Rome. According to this view, only a seven-eighths majority vote would be required. Other members, however, argue that this procedure might lead to the withdrawal by some States Parties from the entire Statute. They favor an entry into force only for the States ratifying the amendment.[14] This would permit the crime of aggression to become operational without requiring the larger seven-eighths majority.

Depending on the subject matter of an amendment, the procedure specified in Article 121 governs amendments. Textual, contextual and teleological interpretation in accordance with the Vienna Convention on the Law of Treaties suggests that paragraph 5 pertains to the crime of aggression. Thus, the amendment will only be binding on those States ratifying or formally accepting the amendment. Even though the crime of aggression has already been listed formally, its definition will substantively constitute an amendment to the crimes. The States Parties, by ratifying the Rome Statute, did not give anticipatory consent to a future definition but rather reserved their right to consent. The definition of the crime had been highly controversial until the finalization of the Rome Statute. It is not the enumeration of aggression among the core crimes, but its definition that is essential to the Court exercising jurisdiction to prosecute the crime.

In other words, the amendment procedure for crimes does not only apply to the adoption of new crimes, but to any regulation related to the crimes for which the ICC has subject matter jurisdiction. The term “amendment” is not restricted to changes in language but also applies to new regulation.[15] Thus, any change, new definition, or amendment to the enumerated crimes, as well as the introduction of new crimes, would require the consent of the relevant States Parties as laid out in Article 121.

There may also be sound reasons to apply the procedure of Article 121(5) to any provision specifying the role of the Security Council. Article 5 aims at a unified regulation that defines the crime of aggression and sets out the conditions for the exercise of jurisdiction. To subject the different provisions of the amendment to different procedures for their entry into force would create an artificial bifurcation, and the combined requirement of the respective procedures (i.e., subjecting the referral procedure to the seven-eighths vote and the definition of aggression to individual ratification) would excessively heighten the threshold for entry into force. The amendment would then only be applicable to those States Parties ratifying the definition provided a total seven-eighths majority ratifies the rules on the exercise of jurisdiction.

Implications for the Jurisdiction of the ICC

The relevance of Article 121(5) for the amendment on aggression has significant implications for the future scope of the ICC’s jurisdiction. It follows from the second sentence of the provision that the Court will only be permitted to exercise its jurisdiction when the crime of aggression was committed on the territory of a State ratifying the amendment and by a national of such a State. The scope of jurisdiction with respect to the crime of aggression will differ from Article 12, which states for the other core crimes that the either the territorial State or the national State must be a Party to the Rome Statute.

Future Structure of the Rome Statute

What does this now mean for the future structure of the Rome Statute, if the State parties adopt the definition of aggression? Since the amendment only enters into force with respect to those States Parties ratifying or depositing an instrument of acceptance, there may end up being two different sets of application: The Rome Statute in its current design would apply to those States Parties that do not ratify or formally accept the amendment. The amended Statute will only apply to those having accepted the amendment one year after the deposit of their instruments of ratification or acceptance.

In order to ensure a uniform text that reflects the differences in application, the adoption of an Additional Protocol to the Rome Statute on the Crime of Aggression could be considered. This method of amendment is common, for example, in the area of human rights and international humanitarian law. The procedure outlined in Article 121(5) could be realized adequately by adopting such an additional protocol. Since the amendment necessitates adjustments with respect to the ratione personae jurisdiction it could be sensible to combine all relevant provisions on the crime of aggression together in one document.


Despite apprehension that aggression will never formally be adopted as a crime subject to the jurisdiction of the ICC, the Special Working Group’s efforts appear to have made progress. The Working Group plans to finalize its work in spring 2009, one year before the Review Conference. Whether the Conference will eventually adopt an amendment is still open and largely depends on political momentum. It is therefore an opportune time for international legal scholars to redirect attention to the legal complexities arising from both the substantive definition of aggression and the procedures through which amendments to the Rome Statute can be made.

About the Author

Anja Seibert-Fohr, LL.M., S.J.D. is the head of the Minerva Research Group at the Max-Planck Institute for Comparative Public Law and International Law in Heidelberg, Germany. She has been teaching International Criminal Law in the M.C.L. Program of Mannheim and Adelaide University.


[1] Rome Statute of the International Criminal Court (adopted July 17, 1998, entered into force July 1, 2002) 2187 UNTS 90, available at (last visited November 14, 2008) [hereinafter Rome Statute].

[2] Rome Statute, Art.5, Para. 2.

[3] See e.g. UN press release of June 6, 2008, available at (last visited November 14, 2008). Report of the Special Working Group on the Crime of Aggression, ICC-ASP/6/20/Add.1 (2008). available at (last visited November 14, 2008)

[4] Art. 6 (a) Nuremberg Charter defined as crimes against peace ”planning, preparation, initiation or waging of a war of aggression, or a war in violation of international treaties, agreements or assurances, or participation in a common plan or conspiracy for the accomplishment of any of the foregoing” (Charter of the Nuremberg International Military Tribunal [proclaimed on 8 August 1945] in United Nations The Charter and Judgment of the Nürnberg Tribunal: History and Analysis [March 3, 1949] UN Doc A/CN.4/5 [United Nations Publications New York 1949]).

[5] For the efforts by the ILC see Yearbook ILC 1950 II, 374; Draft Code of Crimes against the Peace and Security of Mankind, Report of the International Law Commission, Yearbook ILC 1996 II, Part Two, 15 seq.

[6] Resolution ICC-ASP/1/Res.1, Continuity of work in respect of the crime of aggression, available at (last visited November 14, 2008).

[7] American Service-members' Protection Act of 2002, available at (last visited November 14, 2008).

[8] For a detailed account of the Special Working Group’s work see Claus Kress, The Crime of Aggression before the First Review of the ICC Statute, 20 Leiden Journal of International Law 851-856 (2007).

[9] Discussion paper on the crime of aggression proposed by the Chairman (revision June 2008), ICC-ASP/6/SWGCA/2, available at (last visited November 14, 2008).

[10] G.A. Res. 2625, U.N. GAOR, 25th Sess., Supp. No. 28, 121 (Oct. 24, 1970).

[11] Rome Statute, art. 121(5).

[12] Id. art. 121(4).

[13] Id. art. 121(6).

[14] Id. art. 121(5).

[15] The term was used in the context of the United States Constitution when it was supplemented by the Bill of Rights, the first ten Amendments to the United States Constitution.