Traditional doctrine of just ius in bello may be identified in efforts such as of those of the Drago-Porter Convention, the Kellog-Briand Pact, or under the framework of the League of Nations, and even though aggression per se was not susceptible to a legal definition. Since the Nuremberg and Tokyo tribunals aggression has become generally recognized as the ‘supreme international crime’. The customary prohibition that applies to the crime of aggression has as a result extended to include individual liability for international criminal acts.
Aggression was first considered an international crime by the London Agreement in 1945, which was followed one year later by the United Nations (UN) General Assembly decision for adoption of an international criminal code. In addition, in 1974, a General Assembly resolution adopted as the definition of aggression the first and unjustified “use of armed force against the sovereignty, territorial integrity or political independence of another State”. Nevertheless, the political and ideological fears of the Cold War impeded the development of international prescription for aggression.
Recently, while a certain degree of international agreement has been reached on the definition of aggression by a state, the legal blueprint for individual liability of the international crime has remained much divided. In 1994, the International Law Commission, through the General Assembly Ad Hoc and Preparatory Committee on the establishment of an International Criminal Court (ICC), prepared the draft Code of Crimes against the Peace and Security of Mankind. The Code defined aggression as the individual who, as leader or organizer, actively participates in or orders the planning, preparation, initiation or waging of aggression committed by a State, and thus a crime whose definition is dependent on the 1974 definition of state aggression. 
The adoption of a definition of the crime of aggression in the Rome Statute was originally prevented in part by the lack of agreement on whether it should be limited to wars of aggression, or extended to other forms of use of force. In consequence, the jurisdiction of the ICC in crimes of aggression was ‘previewed’ once a definition is reached.
In 2010, the Review Conference of the Rome Statute adopted in Kampala a definition of the international crime of aggression, as well as defined the jurisdictional capacity of the ICC against its perpetration. Both measures are pursued through amendments to the Rome Statute of the ICC and are foreseen to be operational by 2017. 
However, the adoption of the individual definition of aggression appears to continue to clash with the role reserved to the Security Council. The conflict is apparent when it comes to defining the capacity of the ICC to act upon instances of aggression, in the absence of action by the Security Council. The Security Council is the organ of the international community that is primarily responsible for the maintenance of international peace and security, as defined in the UN Charter and recognized in the Rome Statute, and determines the act of aggression and the measures to be applied, as laid down in Chapter VII of the UN Charter. As a consequence, the exclusivity of the Security Council’s role in collective defense appears to be a stumbling block for individual criminal liability on aggression. Nevertheless, no mention can be found in either the UN Charter or the Rome Statute establishing ‘exclusive’ and not ‘primary’ capacity in this area for the Security Council.
All in all, an inclusive ius contra bellum approach could be used to establish a role with regard to matters affecting international peace and security for the General Assembly, and thus grant it competence to determine whether a state has committed an act of aggression. Besides the political organs, the International Court of Justice also has the competence to determine the existence of aggression by evaluating the violation of the prohibition of the use of force as can be seen in the Nicaragua and Oil Platforms cases.
The definition and prosecution of the crime of aggression must be consistent with the above mentioned institutions and instruments. The UN Security Council must be able to respond to acts of aggression and facilitate the mandate of the ICC to prosecute perpetrators. Subsidiary institutional control may also be instrumental for the exercise of competencies over such a controversial matter, and therefore create an international system of checks-and-balances where new bodies such as the UN Human Rights Council should have a say.
In this manner, the international security regime would be reinforced by individual criminal responsibility in cases of international crimes of aggression, and hence would increase the system’s interdependency that could assist to neutralize the incapacities inherited, while in a wider perspective allow the consequent internal renewal.
In other terms, a system adjusted to the contemporary challenges and institutional framework of the new international law.
 C. Kress, The Crime of Aggression before the First Review of the ICC Statute, Leiden Journal of International Law (2007) at 856; A. Cassese, On Some Problematic Aspects of the Crime of Aggression, Leiden Journal of International Law 845.7 (2007).
 General Assembly Resolution 95 (I), Affirmation of the Principles o International Law recognized by the Charter of the Nuremberg Tribunal. General Assembly Resolution 3314, Definition of Aggression.
 A. Cassese, On Some Problematic Aspects of the Crime of Aggression, Leiden Journal of International Law 841-2 (2007).
 Draft Code of Crimes against the Peace and Security of Mankind (1996); Yearbook of the International Law Commission (1996).
 C. Keith, The First Five Sessions of the UN Preparatory Commission for the International Criminal Court, American Journal of International Law 773 (2000); N. Blokker, The Crime of Aggression and the United Nations Security Council, Leiden Journal of International Law 869-75 (2007); F. Kalshoven, L. Zegveld, Constraints on the Waging of War, International Committee of the Red Cross 189 (2001); A. Cassese, On Some Problematic Aspects of the Crime of Aggression, Leiden Journal of International Law 841-3 (2007); Article 5 (2) of the Rome Statute of the International Criminal Court: “The Court shall exercise jurisdiction over the crime of aggression once a provision is adopted in accordance with articles 121 and 123 defining the crime and setting out the conditions under which the Court shall exercise jurisdiction with respect to this crime. Such a provision shall be consistent with the relevant provisions of the Charter of the United Nations”.
 Resolution RC/Res.6 of June 2010; Depositary Notification C.N.651.2010 Treaties-8, of 29 November 2010.
 Article 15 bis (8) and Article 15 ter of the Rome Statute. See also Annex III of Resolution RC/Res.6 of June 2010
 Charter of the United Nations and the Rome Statute of the International Criminal Court.
 Case Concerning Military and Paramilitary Activities in and against Nicaragua (Nicaragua v. United States of America), Merits, Judgment of 27 June 1986; Case Concerning Oil Platforms (Islamic Republic of Iran v. United States of America) Judgement of 6 November 2003.
 R. Clark, Rethinking Aggression as a Crime and Formulating Its Elements: The Final Work-Product of the Preparatory Commission for the International Criminal Court, Leiden Journal of International Law 869-72 (2002); A. Cassese, On Some Problematic Aspects of the Crime of Aggression, Leiden Journal of International Law 843-4 (2007); C. Kress, The Crime of Aggression before the First Review of the ICC Statute, Leiden Journal of International Law 859-63 (2007); N. Blokker, The Crime of Aggression and the United Nations Security Council, Leiden Journal of International Law 876-94 (2007).