The twentieth century began and ended with the execution of genocide. At the same time, it is the century in which large-scale armed conflicts were fought, including the First and Second World Wars. The Second World War was marked, among other things, by genocides committed against peoples that were planned for extermination by Nazi projects. In the first place, it is inevitable to mention the genocide (Holocaust) against the most numerous victims - the Jews. The Holocaust resulted in millions of victims. Mass murders of Jews were carried out, but in the Second World War, about a million people who were members of other nations were also killed. The Nazis carried out the systematic extermination of Jews and other target groups in concentration camps established in Germany, but also in occupied countries. Hundreds of camps were opened throughout the occupied territories of Europe. The target groups scheduled for extermination were collected and transported by trains, most often in transport and livestock wagons, and taken to camps where a certain number were immediately killed, while another number were temporarily left for forced labor. People who were used for forced labor often died of exhaustion, and those who managed to survive the torture were eventually killed. In addition to the closure and liquidation in the camps, individual and mass executions were also carried out in other places. The large number of those killed indicated the need for quick rehabilitation, which resulted in burning the bodies on pyres or burying them in mass graves. The committed genocides encouraged the formation of the United Nations, but also resulted in the adoption of the Convention on the Prevention and Punishment of the Crime of Genocide, or for short - the Genocide Convention, which was supposed to be a guarantee for „never again“. Sanctions issued in the form of death sentences to the most notorious war criminals for the terrible crimes for which they were found responsible should have been another obstacle to „never again“. However, the participants of our time testify that it was not so. Genocidal projects have revived and genocides have been realized, as is the case with the genocide committed in the Republic of Bosnia and Herzegovina at the end of the 20th century. In the trial of the most notorious Nazis, known as the Nuremberg Trials, the harshest death sentences were handed down, as well as life and long-term imprisonment. The specificity of the Nuremberg process is that, in addition to proclaiming the principle of personal responsibility, it also represents a condemnation of the committed aggression, but also a political project as manifested by the condemnation of various organizations that were declared responsible for the crimes committed. At the main international military trial that began on October 18, 1945, 24 defendants were prosecuted for individual responsibility, but six criminal war organizations were also prosecuted - the leadership of the NSDAP (National Socialist German Workers' Party - NSDAP (National Sozialistische Deutsche Arbeiter Partei) headed by was Adolf Hitler - the most responsible criminal for World War II and the execution of the Holocaust), SS (Schutzstaffel - military branch of the NSDAP), SA (Sturmabteilung - Assault Squad of the NSDAP), SD (Sicherheitsdienst - Intelligence Service of the NSDAP), Gestapo (Geheime Staats Polizei - secret state police) and OKW (Oberkommando der Wehrmacht - Supreme Command of the German Army). Certain prosecutions were also carried out in the national courts of the countries that emerged victorious in the Second World War.