From July 7–9, 2025, the Assembly of States Parties (ASP) to the Rome Statute convened a Special Session to address long-standing jurisdictional limitations over the crime of aggression. Despite years of momentum and widespread support from states and civil society, the reform effort failed.
At first glance, the outcome might appear to reflect a legal or normative disagreement, the type of procedural deadlock not uncommon in multilateral treaty bodies. But a neorealist lens offers a compelling framework for analyzing what may lie beneath this surface-level legal or normative disagreement. In a system where states act in accordance with their relative power, the resistance of some powerful states to reform is not incidental, but structural.
A neorealist reading of both the debate and the resolution adopted by consensus at the ASP suggests that the most powerful states have the least to gain, and the most to lose, from broader criminalization of aggression. As long as powerful states can opt out or shape jurisdictional rules, the system remains structurally unequal, smaller and vulnerable states are asked to submit to international justice, while those capable of projecting force shape its contours.
The ASP’s Special Session in New-York: Background, Debate, and Deadlock
Despite being included in the Rome Statute since its adoption, the crime of aggression remains subject to severe jurisdictional limitations. As agreed in 2010 during the Review Conference in Kampala, States Parties committed to reviewing the aggression provisions seven years after their activation. That review was due following the 2017 decision to activate the Court’s jurisdiction over the crime as of July 2018.
The legal inconsistency has become increasingly difficult to ignore. The crime of aggression remains an outlier among the Court’s four core crimes: war crimes, crimes against humanity, genocide, and aggression. Article 15bis (4) and (5) of the Statute enshrine jurisdictional carve-outs that shield powerful states and exclude non-party states, undermining the coherence of the ICC’s legal regime. The result is a gap in enforcement that carries serious consequences, especially for states vulnerable to unlawful uses of force, and has contributed to the persistence of unchecked aggression around the world, ultimately prompting efforts such as the creation of a Special Tribunal for the Crime of Aggression against Ukraine.
After months of preparation and three days of formal deliberation, the ASP failed to consider an amendment proposal and reach consensus on amending the ICC’s jurisdiction over the crime of aggression. The proposal, put forward by Costa Rica, Germany, Sierra Leone, Slovenia, and Vanuatu, aimed to address jurisdictional gaps by replacing Article 15bis (4) and (5) with language based on Article 12 (2) and (3), thereby aligning the Court’s jurisdiction over aggression with its default regime for other core crimes. Most notably, it would have removed existing limitations that significantly constrain the ICC’s ability to act on State Party referrals or initiate proprio motu investigations in aggression cases.
While a significant number of States Parties and civil society actors voiced strong support for harmonizing the crime’s jurisdictional framework with that of the Court’s other core crimes, a smaller but assertive group, including France, Canada, Japan, the United Kingdom, and New Zealand, substantively blocked the reform. States like China and the United States, though not parties to the Rome Statute but present as observer states, opposed the reform. The United States, having imposed sanctions on the ICC, actively, and seemingly successfully, sought to deter any expansion of the Court’s jurisdiction. On the second day of the session, a senior legal adviser to the U.S. State Department delivered a statement threatening to use “all diplomatic, political, and legal instruments to block ICC overreach.”
Although the resolution adopted at the close of the Special Session includes language that could facilitate future reform, such as the establishment of a stocktaking meeting in 2027 and a follow-up Special Session in 2029, it ultimately reflected the deep structural divisions among States Parties. The resolution acknowledged this divide explicitly:
“Recognizing that many States Parties take the view that there is a gap in jurisdiction over the crime of aggression and advocate for harmonization… Also recognizing that other States Parties take the view that the current provisions reflect a balance agreed at Kampala and confirmed in 2017…”
While diplomatically worded, this language captures the political stalemate that continues to hinder reform. What appears to be a technical or legal disagreement is, in structural terms, a predictable expression of the power asymmetries that define international lawmaking. This is precisely the dynamic that neorealism helps illuminate.
Who Supports Reform and Why: A Structural Explanation of the ASP Divide
The ICC Assembly’s failure to reform the crime of aggression is not merely a political outcome, it is a structural expression of international power. The outcome is best understood through the lens of structural realism, particularly the theory developed by Kenneth Waltz, which asserts that international outcomes are shaped not only by morality or institutional design, but primarily by the distribution of capabilities (power) among states. In other words, structure conditions behaviour, and in an anarchic international system, where there is no ‘world government,’ it is power that conditions structure.
As Waltz argues, international politics cannot be fully understood by looking only at state preferences. The causes of international outcomes “run in two directions”: from states to outcomes, but also from structure to states. Without accounting for the structural dimension, explanations risk being partial or misleading. This dual-level analysis helps explain why some politically diverse states resisted reform, while others, such as Sierra Leone, Chile, the State of Palestine, or Timor-Leste, actively supported it.
While various factors such as morals, values, ideology, domestic politics, or institutional preferences may influence state behavior, neorealism centers power due to its central explanatory value in a self-help international system. States are positioned differently based on their power. Thus, states are shaped not only by who governs them, but by the conditions they all face: anarchy and the unequal distribution of power. Even if some states support legal reform for moral or ideological reasons, their choices are still influenced by how secure or vulnerable they are within the system.
Interestingly, the division did not follow a simple North–South or ideological line. Rather, it reflected what structural realism would predict: states with greater global influence and military capabilities were more likely to resist legal limits on the use of force, while structurally weaker states supported reforms to strengthen legal protections. In a neorealist reading, where the international system is defined by anarchy and unequal power, it is the distribution of capabilities, not just shared values, that often conditions legal outcomes.
This may help explain why even democratic or law-abiding states occasionally resist efforts to expand the Court’s jurisdiction. In such cases, it may be less about normative commitments and more about structural positioning. As Waltz notes, in an anarchic international system, the “logic of anarchy obtains” regardless of whether the actors are nation-states, tribes, or corporations, the defining feature is that each unit must ultimately rely on itself for security. From this perspective, legal reform may appear more urgent or desirable to states lacking the material power to deter aggression, while those with significant capabilities may see less strategic incentive to constrain their own freedom of action.
Small or structurally vulnerable states, such as Timor-Leste, the Democratic Republic of the Congo, Vanuatu, Nigeria, Ukraine, Ghana, Armenia and Senegal, supported reform. For these states, strengthening the ICC’s jurisdiction over aggression is not abstract legal idealism but a concrete strategy for survival in a system that offers little deterrence against unlawful force.
This support reflects structural necessity rather than ideological alignment: they are responding to their limited ability to deter or repel aggression on their own. These states seek an international order where legal norms constrain the use of force precisely because they are the ones most exposed when those norms break down.
A System That Fails the Vulnerable
The ASP’s failure to amend the Kampala Amendments and harmonize the jurisdiction over the crime of aggression is often framed as a legal disagreement, a matter of jurisdictional complexity or competing legal visions. But from a structural perspective, it is better understood as the consequence of systemic power imbalances. In a neorealist framework, states prioritize their own security, and for powerful states, strategic autonomy is a central component of that security. Expanding the ICC’s jurisdiction over aggression would place real legal constraints on the ability to use force, a tool which powerful states rely on.
For small states, the session’s outcome was more than a missed opportunity. It was a pointed reminder that the international institutions they rely on for justice and deterrence are often subject to the political will, or resistance, of more powerful actors. In this sense, the ASP’s failure is not only legal in nature but deeply structural.
As Waltz reminds us, even decades after he first articulated his theory, international systems are not held together only by values or shared ideals. Otherwise, the constant calls from states and civil society to finally amend the Kampala Amendments, to not let what was once called in Nuremberg in 1945 “the accumulated evil of the whole”, would have convinced them.
Yet the failure to adopt meaningful reform ultimately preserves a system that offers the least protection to those most at risk. In this sense, the Special Session did not just stall legal progress, it failed the states that depend on international law for their very existence.
