Before World War II, French Indochina little concerned American policymakers. The idea of sending half a million men to fight a war there would have seemed as fantastic as sending a man to the moon. Even after John F. Kennedy decided that the United States should - and could - send a man to the moon, the idea of sending half a million men to Vietnam still seemed fantastic. When George Ball expressed fears that such a possibility indeed existed if matters were allowed to continue until incremental creep became an avalanche, the president was astounded. ‘George’, Kennedy admonished him, ‘you're just crazier than hell. That just isn't going to happen.’ Historians still debate whether Kennedy would have followed the same path Lyndon Johnson took in Vietnam, thereby fulfilling George Ball's seemingly absurd prophecy. My purpose here is not to rehearse the arguments in that debate. Instead, I want to talk about the American ‘cause’ in Vietnam, and how, beginning in World War II, a generalised concern with the problem of closed economies and the creation of a post-colonial world order finally became focused on Vietnam.