The crime of aggression only began to be judged by the International Criminal Court in 2019, one year after it was regulated, because before that, there was no precise definition of what this type of crime would be, which today makes up Article 8 of the Rome Statute and is defined by being actions organized by a political or military representative and that endanger the sovereignty or territorial integrity of another state, thus contradicting the principles of the UN Charter. In this way, the crime of aggression occurs only when high-ranking representatives of the state plan and demand the execution of the crime.

With the Kampala conference, which took place in 2010, members of the International Criminal Court began to discuss the crime of aggression. Still, it was only in 2017 that the Kampala amendment became official, which required time for the law to start to be used definitively to bring those responsible for such a crime to trial. Another requirement of the Kampala amendment is that the International Criminal Court only tries crimes of aggression if all states involved are parties to the Rome Statute.

This means that the International Criminal Court cannot try these crimes of aggression if they involve nationals or territories of states that have not accepted the jurisdiction of that court, even if they involve a state party. This turns out to be an incentive to ratify the constituent instrument of the International Criminal Court to gain access to the Court.

Therefore, states that do not ratify the Kampala amendment cannot prosecute or be tried for the crime of aggression, even if they are member states. And further, if the state approves the amendment and makes the "opt-out," which is an express declaration that they do not accept that their nationals be tried for the crime of aggression, then they can prosecute nationals of other countries that have ratified without making the opt-out, but they cannot be charged.

The exception to this rule is that the UN Security Council can take cases of crime of aggression to be tried by the International Criminal Court, even if it has not been committed by member states and without regard to the ratification of the Kampala amendment. Still, the International Criminal Court may or may not refuse the case.

It can be observed that the trial of the crime of aggression is more complex when compared to the crime of genocide or war crimes. The most likely reason for this bureaucracy is that aggression is a person must have committed by a person in a high position. In this regard, the Court may come to exercise its jurisdiction over the crime of aggression once it has proved a provision in which the crime is defined, and the conditions under which the Court itself will have jurisdiction over this crime are announced. Such a provision, however, must be compatible with the relevant provisions of the United Nations Charter.

Articles 121 and 123 of the Rome Statute establish the crime of aggression as an attack on a state's sovereignty, territorial integrity, or political independence. The crime of aggression may resemble the crime against peace, which is found in the Treaty of Versailles and alleges the directing, preparing, waging, or continuing of war or aggression or a war in violation of international treaties, guarantees, or agreements.

Examples of the crime of aggression include bombings, port blockades, sending regular or paramilitary soldiers into another country, and political leaders and chiefs who can be held individually responsible for starting a conflict by not following the rules of international criminal law.