"The notion that every state has an interest in the territorial integrity of every other state-no matter how distant they are and how slight their connections-is peculiar to the twentieth century. To be sure, poets and philosophers had perceived humanity's common interest in preventing wars, and statesmen had found that aggression from outside the community could be deterred by the mutual defense of those within it. But no one had ever tried to organize an all-embracing system that used the collective force of its members to prevent one of them from attacking another.It took the wide devastation of two world wars-and the failure of the balance-of-power systems that preceded them-to instigate the search for a more effective way to manage power. To the founders of the League of Nations and the United Nations there was nothing extravagant about the idea that peace is indivisible. Their countries had been drawn into wars that were largely not of their making: They had learned that to control their destinies they must act early, with others, to keep the peace. It is this core of national self-interest that drives collective security. If the system works at any moment in history, it is because its members believe they have enough stake in the existing order to warrant taking measures against any nation that threatens to destroy the fabric of that order. "