Crime of aggression

Definition and Treaty Law

The crime of aggression has evolved significantly from its origins in post-World War II international law. Initially defined in Article 6(a) of the Charter of the International Military Tribunal at Nuremberg as "planning, preparation, initiation or waging of a war of aggression," the crime was described by the IMT in its 1946 judgment as "the supreme international crime differing only from other war crimes in that it contains within itself the accumulated evil of the whole."

The Rome Statute Framework

Article 5(1)(d) of the Rome Statute initially included the crime of aggression within the International Criminal Court's jurisdiction but deferred its activation pending the adoption of a definition and jurisdictional conditions. This gap was addressed at the 2010 Kampala Review Conference, which adopted comprehensive amendments defining the crime.

Under Article 8 bis of the Rome Statute (as amended), the crime of aggression is defined as:

"The planning, preparation, initiation or execution by a person in a position effectively to exercise control over or to direct the political or military action of a State, of an act of aggression which, by its character, gravity and scale, constitutes a manifest violation of the Charter of the United Nations."

The provision further defines an "act of aggression" as "the use of armed force by a state against the sovereignty, territorial integrity or political independence of another state, or in any manner inconsistent with the Charter of the United Nations." This incorporates the same acts enumerated in UN General Assembly Resolution 3314 (XXIX), including invasion, bombardment, blockade, and the use of armed bands or mercenaries.

Key Features of the ICC Definition:

• Leadership requirement: Only persons who can "effectively exercise control over or direct the political or military action of a State" can be prosecuted
• Manifest violation standard: The act must constitute a "manifest" violation of the UN Charter by its character, gravity, and scale
• Complex jurisdictional regime: Different procedural requirements apply depending on whether the situation is referred by the UN Security Council, a State Party, or initiated by the Prosecutor

The Kampala amendments entered into force on 17 July 2018, following ratification by the required 30 states and activation by a two-thirds majority of the Assembly of State Parties in December 2017.

Customary International Law Status

The International Court of Justice (ICJ) has held that the prohibition of the use of force as contained in the UN Charter is a norm of customary international law. It is also widely accepted that this prohibition has reached the status of jus cogens (a peremptory norm of international law).

Likewise, it is generally accepted that the crime of aggression constitutes a crime under customary international law. In 2006, the UK House of Lords concluded that the crime of aggression was recognised as a crime under customary international law by the end of the 20th century. This recognition builds upon the Nuremberg and Tokyo precedents, which established the principle that aggressive war constitutes an international crime for which individuals can be held accountable (Benchbook, para. 961).

Hence, the customary law foundation for the crime of aggression is well-established, but questions remain about its precise scope and elements.

Relationship with UN Charter Framework

The customary crime of aggression builds upon the well-established prohibition on the use of force between states, transforming it from purely state responsibility to individual criminal liability. UN General Assembly Resolution 3314 (XXIX), while not creating criminal liability itself, has been widely accepted as reflecting customary international law regarding what constitutes an act of aggression between states.

The Rome Statute's definition in Article 8 bis represents an attempt to codify and clarify the customary crime, though questions remain about whether all elements of the Rome Statute definition reflect established customary law or constitute progressive development of international law.