In the last two centuries, the world and humanity have changed more than ever. The rapid development of technology, but also socio-humanistic and political thought has led to a completely different perception of the world by people. The desire to spread influence, aided by technological development, has pushed the great powers into the bloodiest armed conflicts the world has ever seen. After the end of the First and Second World Wars, it proved necessary not only to sanction the leaders of the idea of aggressive war, but also to sanction the insult to the independence of countries through the armed attack. In this regard, the international community has approached a more detailed definition of the concept of aggression and crimes against peace (crime of aggression) and the establishment of appropriate mechanisms with the aim of preventing armed conflicts, stopping them and promoting peaceful settlement of international disputes. It is this idea that is the subject of the text that follows. The author wants to make his modest contribution to legal science in terms of analysis of the concept of aggression in international law (primarily in international public law), but also the definition and elements of (international) crime – crime against peace (aggression) in international criminal law. In addition to explaining and clarifying the content of the concept of aggression, the author will analyze this international crime contained in international documents, present the jurisdiction of the International Criminal Court in relation to aggression, and explain the position and role of the United Nations in preventing armed conflict and peace. Finally, a critical analysis of all the above, the author will present the advantages and disadvantages of mechanisms for preventing armed conflict and punishing perpetrators of international crimes against peace through the prism of the amendment to the Rome Statute of the ICC.