This study showed the difficulties faced to reach an agreed definition of the crime of aggression since the establishment of the League of Nations in 1919 until the establishment of the International Criminal Court in 1998. In fact, these difficulties are still very problematic even after reaching a definition of this crime in the First Review Conference of the International Criminal Court, which held in Kampala in 2010, either because of the many loopholes contained in this definition or the different interpretations put forward by international jurisprudence around.

This study has concluded that the definition of the crime of aggression, although seen as a right step for the development of the rules of international criminal law and to prevent impunity, but determination what constitutes an act of aggression seems extremely difficult, especially if we taking into account the authority of the U.N. security Council which is mostly based on political considerations.

The challenge over the efficacy of this new-old definition of the crime of aggression will be related to the decision should be taken by the Assembly of States Parties to the Court after 1st of January 2017, and the practice of the Court to look at the first crime of aggression.