War crimes, crimes against humanity, genocides, indiscriminate massacres and atrocities. We've seen them all. We've seen them in places and countries around the world. Ancient and modern history are full of them.

Still, it was only relatively recently that such horrendous crimes were liable to be investigated, prosecuted and judged. The majority of those behind such barbaric acts were never brought to justice and continued roaming freely.

The first real trials for such crimes against humanity took place in Nuremberg between 1945 and 1949. They marked the first-ever prosecutions for genocide and crimes against humanity. In addition to bringing some of Nazi Germany's most monstrous figures to justice, the Nuremberg Trials broke new ground in international law and helped lead to the United Nations Genocide Convention (1948), the Universal Declaration of Human Rights (1948) and the Geneva Convention on the Laws and Customs of War (1949).

International public law was taking shape and some world order was being established. Until the Nuremberg Trials, there had been no precedent for an international trial of war criminals. Rather than use a single judge and jury, the trial of high-ranking Nazi leaders was conducted by a panel of four judges. The United States, Soviet Union, France and Great Britain each supplied a main judge and an alternate, and Britain's Lord Justice Geoffrey Lawrence presided.

Some of the most heinous crimes were committed during the conflicts that marked the twentieth century. In 1948, the United Nations General Assembly recognised the need for a permanent international court to deal with the kinds of atrocities that had just been perpetrated. However, it was only after the end of the Cold War that the idea of a system of international criminal justice reemerged.

While negotiations on a system of international criminal justice were underway at the United Nations, the world was witnessing the commission of heinous crimes in the territory of the former Yugoslavia and in Rwanda. In response to these atrocities, the United Nations Security Council established an ad hoc tribunal for each of these situations.

These events undoubtedly had the most significant impact on the decision to convene the conference of 160 states, which established the International Criminal Court (ICC) in Rome in the summer of 1998. Among other things, the Rome Statute of the International Criminal Court sets out the crimes falling within the jurisdiction of the ICC, the rules of procedure and the mechanisms for states to cooperate with the ICC.

Over 120 countries are parties to the Rome Statute, representing all regions: Africa, the Asia-Pacific, Eastern Europe, Latin America and the Caribbean, as well as Western Europe and North America. The seat of the court is in The Hague, in the Netherlands. The Rome Statute provides that the Court may sit elsewhere whenever the judges consider it desirable. The Court has also set up offices in the areas where it is conducting investigations.

But perhaps the most salient feature is that the ICC is a permanent international court established to investigate, prosecute and try individuals accused of committing the most serious crimes of concern to the international community as a whole, namely the crime of genocide, crimes against humanity, war crimes and the crime of aggression, and that were committed on or after July 1, 2002.

The 15 forms of crimes against humanity listed in the Rome Statute include offences such as murder, rape, imprisonment, enforced disappearances, enslavement, particularly of women and children, sexual slavery, torture, apartheid and deportation.

As of July 17, 2018, a situation in which an act of aggression would appear to have occurred could be referred to the Court by the Security Council, acting under Chapter VII of the United Nations Charter, irrespective of whether it involves States Parties or non-States Parties.

A "crime of aggression" means the planning, preparation, initiation or execution of an act of using armed force by a state against the sovereignty, territorial integrity or political independence of another state. The act of aggression includes, among other things, invasion, military occupation, and annexation by the use of force or blockade of the ports or coasts, if it is considered, by its character, gravity and scale, a manifest violation of the Charter of the United Nations. The perpetrator of the act of aggression is a person who is in a position effectively to exercise control over or to direct the political or military action of a state.

The ICC prosecutes individuals, not groups or states. Any individual who is alleged to have committed crimes within the jurisdiction of the ICC may be brought before the ICC. In fact, the Office of the Prosecutor's prosecutorial policy is to focus on those who, having regard to the evidence gathered, bear the greatest responsibility for the crimes and does not take into account any official position that may be held by the alleged perpetrators.

In some circumstances, a person in a position of authority may even be held responsible for crimes committed by those acting under his or her command or orders. Likewise, amnesty cannot be used as a defence before the ICC. As such, it cannot bar the Court from exercising its jurisdiction.

But with only 10 successful convictions in a quarter of a century, has it been useful? International criminal justice remains a work-in-progress, but the ICC represents the best chance of continuing the principles brought to life by the UN tribunals.

Dr Mark Said is a lawyer