Reluctant ratifiers: The crime of aggression at the International Criminal Court

A unanimous agreement among state parties to the Rome Statute of 1998 to make the crime of aggression an operational part of the Rome Statute and the International Criminal Court (ICC) was the key result of the first Review Conference for the Statute in June 2010 in Kampala, Uganda. Yet, as of December 2024, only forty-six of the 125 state parties to the Rome Statute have ratified the Kampala Amendments. Our paper seeks to identify the political conditions that may have contributed to this limited follow-through by Rome Statute members on the crime of aggression. We find that the Amendments have been accepted by Rome Statute signatories that have shown a low propensity to initiate military disputes; face less threatening security environments; and are wealthy, democratic, and follow domestic legal traditions that make it less costly to join international treaties. The Kampala experience demonstrates once more that states exercise great political discernment in electing to adhere to international laws, and are reluctant to embrace agreements that entail a gap between provisions in them and their foreseeable future conduct.