For centuries, conducting war was regarded as one of the most important attributes of state sovereignty. With the development of international relations, technology and human capabilities, which repeatedly led the fate of humanity to the end, the approach to the conduct of war as foreign policy began to evolve into a pacifist outlook. The achievement of the moment of 1928 was when the Brianda-Kellog Pact was for the first time enacted, and an absolute prohibition of aggressive warfare was preceded by stages in which the states formed, in small steps, the awareness of the need to change their approach to war. The very fact of introducing its prohibition did not save the world from the outbreak of World War II, but it allowed the prosecution of war criminals, and forever changed the approach to war. Since then, although the world is not free from armed conflict, the states resorting to the use of force must find a justification for their actions on the basis of norms of international law.