The work is devoted to the characterization of the legal nature of war as a social phenomenon, its place in the legal system of society, its significance for the history of law in general, and Ancient Russian law in particular. Special attention is paid to the characterization of the genetic origins of war from the point of view of legal anthropology. The article presents systematic data on Byzantine religious and legal norms that could have influenced the evolution of ancient Russian legal customs that regulated war as a special law enforcement tool.