This book deals with world peace, analysed according to Hans Kelsen's pure theory of law and Sigmund Freud's theory, in this case in response to a letter from Albert Einstein on the subject. Freud states that man wages war driven by an inner destructive impulse, and that only the strengthening of its opposite, the vital eros of life, would counteract its aggressive force. This work analyses this thesis in the light of international law according to Kelsen's normativism, for whom world peace can only be ensured by the establishment of a sovereign world state, capable of coercively applying its decisions to national states in conflict, which would resolve their disputes by resorting not to war but to higher international judicial bodies. This notion prefigures what is now called communitarianism, the basic doctrine of the construction of legally unified blocs of nations, whose greatest exponent today is the thinker Michel Sandel.