Killing members of this group

Genocide
Genocide — acts committed with the intent to destroy, in whole or in part, any national, ethnic, racial or religious group as such by:

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  killing members of this group;
  
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  causing serious harm to their health;
  
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  measures designed to prevent childbearing in such a group;
  
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  forced transfer of children;
  
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  deliberate creation of living conditions designed for the complete or partial physical destruction of this group.
  

Since 1948, genocide has been recognized by the UN as an international crime.
There are many cases of genocide in the history of mankind, starting from ancient times and up to the present day.
This is especially true for wars of extermination and devastating invasions, campaigns of conquerors, internal ethnic and religious clashes, for the formation of colonial empires of European powers. The term "genocide" was first coined in 1943 by Raphael Lemkin, a Polish lawyer of Jewish origin, and it received international legal status after World War II in December 1948 ("Convention on the Prevention and Punishment of the Crime of Genocide") as a concept defining the gravest crime against humanity.
Therefore, in order to prevent legal and logical conflicts, the use of the term by some lawyers is considered justified only in relation to events after 1948. "Legal advisers argue that the Convention does not contain provisions that would allow its retroactive application. On the contrary, they say, the Convention unequivocally proceeds from the fact that its purpose is to impose obligations only on the participating States and only for the future."
On the other hand, "Article 28 of the Vienna Convention on the Law of Treaties, to which they refer in support of the thesis that "international law generally prohibits the retroactive application of treaties," does not exclude the retroactive effect of treaties at all, but only determines this by the desire of the parties to the treaty. The Vienna Convention on the Law of Treaties entered into force on January 27, 1980, that is, after the entry into force of the Genocide Convention.
Therefore, if we follow the logic of legal advisers, it does not apply to the earlier Genocide Convention." The first edition of the "Convention..." also included political assassinations in the definition, but the USSR and some other countries did not agree to consider actions directed against groups identified by political or social characteristics as genocide. Therefore, for political and diplomatic reasons, these groups were excluded from the "Convention...".
<...> I identified myself more and more with the sufferings of the victims, whose number grew as I continued to study history. I realized that memory is not only designed to register the events of the past, but also to stimulate a person's conscience. Modern examples of genocide soon followed, such as the massacre of Armenians in 1915. It became clear to me that the diversity of nations, religious groups and races is important for civilization, because each of these groups is called upon to fulfill a mission and contribute in terms of culture. <...> I decided to become a lawyer and achieve the prohibition of genocide and its prevention by combining the efforts of the countries and — Rafael Lemkin.