Reviewing the Crime of Aggression: A Defining Moment for International Criminal Law

Next week, from the 7th to the 9th of July, State Parties to the Rome Statute will convene in New York. The countries that have ratified the founding treaty of the International Criminal Court (ICC) – which defines the Court’s jurisdiction and powers – will convene for a critical review on the crime of aggression, one of the four core crimes in the Rome Statute. The meeting will revisit, and potentially redefine, how the ICC can take cases against, and prosecute leaders responsible for the unlawful use of force between states.

The Crime of Aggression

Russia’s full-scale invasion of Ukraine in 2022, and the continuation of that war alongside other major armed conflicts around the world, have become defining features of the current geopolitical landscape. These developments underscore the need for robust international mechanisms to hold those responsible for acts of aggression to account.

Under the current legal framework, the ICC’s ability to prosecute the crime of aggression is significantly constrained. The Court lacks jurisdiction when non-States Parties are involved — either as aggressors or victims — unless the case is referred by the UN Security Council, a mechanism that is both highly politicized and rarely invoked. Additionally, State Parties may opt out of the Court’s jurisdiction over aggression. As a result of these constraints, ad hoc tribunals have been the only recourse available to address such actions when the aggression is perpetrated by non-States Parties. This stands in stark contrast to the ICC’s jurisdiction over genocide, crimes against humanity, and war crimes — none of which face the same legal limitations.

This highlights a fundamental inconsistency in international law, one that many, including civil society coalitions and legal experts, hope the upcoming review will begin to close. Jennifer Trahan, Convenor of the Global Institute for the Prevention of Aggression (GIPA) says that although ad hoc tribunals are important, “there also must be a Rome Statute amendment”, adding that “these two processes must work in tandem in order to avoid selective justice.” For GIPA and like-minded advocates, achieving justice in the case of Russian aggression against Ukraine is vital, but so is ensuring that accountability for this crime is not selective or exceptional.

The Global Challenges Foundation has been supporting the efforts of two key actors in the lead-up to the Review Conference: GIPA and the European Center for Constitutional and Human Rights (ECCHR). Both organisations have played central roles in pushing for a harmonisation of the ICC’s jurisdiction over the crime of aggression, aiming to align it with the Court’s existing authority to prosecute genocide, war crimes, and crimes against humanity.

The Long Road to Recognition

When the Rome Statute was adopted in 1998, states failed to reach consensus on how to define the crime of aggression. Unlike the other core crimes – genocide, war crimes and crimes against humanity – which were were defined already in 1998, aggression became a political minefield. Powerful states, particularly the permanent members of the UN Security Council, were reluctant to give jurisdiction to the ICC to prosecute acts of aggression, fearing that it could constrain their own political or military aims and decisions. 

At the 2010 Review Conference of the Rome Statute in Kampala, states finally managed to agree on a definition and on the conditions under which the ICC could exercise jurisdiction. However, the outcome – the so-called Kampala amendments – was a political compromise: states were permitted to opt out of the Court’s jurisdiction over aggression, and the ICC was barred from proceeding with cases involving non-state parties without a UN Security Council referral. In other words, unlike the other Rome Statute crimes, the ICC’s ability to prosecute aggression was heavily restricted from the outset, with further restrictions imposed in 2017.

Arne Bardelle, Senior Legal Advisor in the International Crimes and Accountability program at ECCHR says “the limitations on the ICC’s jurisdiction over this crime, represent a glaring double standard, one that is rooted in the efforts of powerful states to shield themselves from accountability.” As of July 17, 2018, the Court’s jurisdiction over the crime of aggression was activated, and since the 2010 Kampala Conference, 48 States Parties have ratified the amendments. Importantly, the Kampala conference included a provision mandating a review seven years after activation, recognising that the jurisdictional arrangements for aggression might need reassessment. That provision is what has brought us to the 2025 Review Conference.

A Path Toward Harmonisation

The upcoming Review in New York presents a rare and critical opportunity to address the long-standing discrepancies in the ICC’s jurisdiction over the crime of aggression. A proposed amendment, submitted by Costa Rica, Germany, Sierra Leone, Slovenia, and Vanuatu, aims to harmonise the Court’s jurisdiction over aggression with that of the other three core crimes. The amendment would remove the opt-out clause and allow the ICC to proceed with cases where either the territory where the crime was committed or the nationality of the accused falls within its jurisdiction.

However, harmonisation remains far from assured.  Several states, including major powers – many of them Western – have continued to express concerns over technical details or potential geopolitical implications. Even within regions that are generally supportive of reform, there is no uniform stance, reflecting the broader tensions surrounding this issue.

Progress has been slow and often frustrating. David Donat Cattin, Senior Fellow of the Montreal Institute for Global Security (MIGS), notes that only in recent years have large human rights NGOs begun to engage with the issue and express support for increased jurisdiction for the ICC over the crime of aggression. “They are supportive of the amendment as a matter of equality of all before the law. They see it as a fixing of the jurisdiction of the court, harmonising and aligning with the other core crimes”.

In the lead-up to the conference, both GIPA and ECCHR have engaged in extensive outreach to state parties and civil society organisations to build momentum and increase awareness. GIPA has hosted multiple regional workshops around the world and just a few weeks ago, organised a key event at the African Union Mission in New York. This work has let GIPA impart their judicial expertise and knowledge from 25 years of working with the crime of aggression to regions previously underrepresented in discussions of this issue. ECCHR, meanwhile, has coordinated a growing network of civil society groups, circulated legal briefings, and gathered over 80 endorsements for a joint civil society statement calling for reform. 

It is of vital importance that civil society is actively engaged in these processes, not least because it often represents and amplifies the voices of the populations most directly affected. Inclusive processes are essential, as it is the people in countries under attack who bear the greatest burden of the crime of aggression — a crime that frequently marks the beginning of further atrocities such as genocide, war crimes, and crimes against humanity.

A Defining Test of Commitment

This July’s Review Conference provides a chance for the international community to prove its commitment to justice without exception. The proposed amendment to harmonise the ICC’s jurisdiction over the crime of aggression offers a pragmatic yet principled solution to address a glaring gap in the architecture of international criminal law.

While the ICC has faced challenge to its credibility and political backlash from powerful actors, the Court itself has “done more in the last three and a half years than in the last 18” said David Donat Cattin, referring to cases involving the Myanmar military commander, Taliban leaders, the Russian Federation President and the Israeli Prime Minister. 

In an era of rising authoritarianism, open warfare, and declining trust in multilateralism, harmonising the Court’s jurisdiction over the crime of aggression is not just about closing a legal loophole. It is about reaffirming the principle that no leader is above the law — and that those waging aggressive war should face accountability, regardless of geography or power. As Arne Bardelle noted, “If Western states are serious about supporting a rules-based order, they must back this amendment unequivocally.”