A farewell is given to something that is leaving. After thousands of years of freedom for nations to go to war, new proximity, interdependence, risks of nuclear war have led them to exercise restraints and to commit themselves to the UN Charter and the requirement to abandon interstate uses of force. This book concludes that while states will continue as always to compete, the great powers are saying farewell to direct interstate wars. For over 75 years there have been no wars between them and no nuclear weapon has been used. The Charter as rule-based international order has often been violated and the veto has often stood in the way of action. Yet, the General Assembly has asserted the order and declared that it does not recognize illegal annexations. The nuclear arsenals remain and pose existential risks to humanity. At the same time, the fear that they would be used in second strikes makes it implausible that any nuclear-armed states would initiate hostilities that could risk leading to nuclear war. Russia’s aggression in Ukraine is seen as out of tune with the twenty-first century – an aberration. The growing interdependence of states is creating restraints against causing ruptures and, at the same time, enables states to use crippling economic measures as substitutes for the use of force. In 1962, the Cuban missile crisis shocked the parties and prompted them to use diplomacy to avert the acute risk of nuclear war. Today, one may speculate if the war in Ukraine and threats to the human environment might shock nations to turn to diplomacy and disarmament and switch to the defence of the threatened human environment a major part of the some 2 trillion dollars that they now spend annually to defend themselves against each other. For this to become reality, an engaged public mind would be as important as it was against slavery and nuclear weapons.